DESCRIPTION Title of Invention: HETEROCYCLIC COMPOUND Technical Field [0001] The present invention relates to a heterocyclic compound which is useful as an active ingredient of a pharmaceutical composition, for example, a pharmaceutical composition for preventing and/or treating phosphatidylinositol-3-kinase 8 (PI3K5)-related diseases. Background Art [0002] Phosphatidylinositol-3-kinase (PI3K) is a lipid signaling kinase, which is present universally throughout species, ranging from plants or yeasts to mammals including humans. PI3K is an enzyme for phosphorylating the hydroxyl group at the 3-position of phosphatidylinositol, phosphatidylinositol-4-phosphate, and phosphatidylinositol-4,5-diphosphate, which are cell membrane phospholipids, and from each of these substrates, phosphatidylinositol-3 -phosphate, phosphatidylinositol-3,4-diphosphate, and phosphatidylinositol-3,4,5-triphosphate (PIP3) are produced. These phosphorylated phosphatidylinositols thus produced act as an intracellular second messenger. Particularly, PIP3 causes migration of various molecules having pleckstrin homology (PH) domains to a position near the cell membrane to induce activation of the molecules, and thus it is considered to be the most important phosphorylated phosphatidylinositol ("The Journal of Biological Chemistry", 1999, Vol. 274, p. 8347-8350). [0003] PI3K is divided into three classes, Classes I, II, and III, according to various characteristics, and from the viewpoints that the only enzyme producing PIP3 in vivo is Class I PI3K, the Class IPI3K is considered to be the most important class ("Biochimica et Biophysica Acta", 2008, Vol. 1784, p. 159-185). The Class I PI3K is subdivided into IA and IB. The Class IA PI3K consists of heterodimers including a combination of a 110-kDa catalytic subunit (pi 10a, p, or 5) and a 50- to 85-kDa regulatory subunit (p85a, p85p\ p55a, p55y, or p50a), and the Class IB PI3K is a heterodimer of a 110-kDa catalytic subunit (pllOy) and a 101-kDaregulatory subunit (plOl) ("Nature Immunology", 2003, No. 4, p. 313-319). Hereinafter, the respective names of PI3K are referred to as PI3Koc, |3, 8, and y, corresponding to catalytic subunits included therein. [0004] PDKa and P are widely present in a biological body and deficiency of PBKa and (3 in mice has been reported to be fetally lethal in both cases ("The Journal of Biological Chemistry", 1999, Vol. 274, p. 10963-10968; and "Mammalian Genome", 2002, Vol. 13, p. 169-172). As a result of studies using subtype selective compounds, it has been reported that PI3Ka plays an important role in insulin signaling and a PI3Ka inhibitor causes insulin resistance ("Cell", 2006, Vol. 125, p. 733-747). Further, it has been reported that PI3K(3 is involved in platelet aggregation and a PI3K(5 inhibitor has an antithrombotic effect ("Nature Medicine", 2005, Vol. 11, p. 507-514). On the other hand, mice deficient in PI3K5 or y are all born normally, and no problems concerning growth, life span, reproduction, or the like have been found ("Science", 2000, Vol. 287, p. 1040-1046; and "Molecular and Cellular Biology", 2002, Vol. 22, p. 8580-8591). In particular, expression of PI3K8 is significantly limited to hemocytes and lymphoid tissues, and mice deficient in PI3K8 have been found to have significant damage in activation of lymphocytes. A close relationship between the activation of lymphocytes and immunity/inflammation is well known, and compounds selectively inhibiting PI3K5 have a potential to be immunity/inflammatory inhibitors having both a potent inhibitory action on the activation of lymphocytes and safety. [0005] Interleukin-2 (IL-2) is a kind of cytokine which is mainly produced from activated T cells. IL-2 induces proliferation and activation of lymphocytes via an IL-2 receptor which is a receptor for IL-2. IL-2 is a very important molecule in signaling the activation of an immune system, and its production inhibitors (for example, Tacrolimus and Cyclosporin A) have been used clinically as immunosuppressing agents. In addition, anti-IL-2 receptor monoclonal antibodies such as Basiliximab and Daclizumab have been used clinically as immunosuppressing agent. [0006] B cells are one of the main subsets of lymphocytes, along with T cells, and are cells which is a main actor of humoral immunity. It is known that humoral immunity plays an extremely important role in preventing infection from pathogens or the like, but in autoimmune diseases such as rheumatoid arthritis and the like, abnormal activation of humoral immunity occurs, which is deeply involved in the pathogenesis. In fact, an anti-CD20 antibody, Rituximab, has been used clinically as a drug for treating rheumatoid arthritis. [0007] As the compound having a PI3K inhibitory action, for example, the compounds of the formula (A-l) (Patent Document 1), the formula (A-2) (Patent Document 2), the formula (A-3) (Patent Document 3), the formula (B-l) (Patent Document 4), the formula (B-2) (Patent Document 5), the formula (B-3) (Patent Document 6), the formula (C) (Patent Document 7), the formula (D-l) (Patent Document 8), the formula (D-2) (Patent Document 9), the formula (E-l) (Patent Document 10), the formula (E-2) (Patent Document 11), the formula (E-3) (Patent Document 12), the formula (F) (Patent Document 13), the formula (G) (Patent Document 14), the formula (H) (Patent Document 15 and Non-Patent Document 1), the formula (J) (Patent Document 16), and the formula (K) (Patent Document 17) described below have been reported. However, the compound of the formula (I) of the present application as described later is different in the structure of the group R1 of the formula (I) from the compounds of the formulae (A-l) to (E-3), (H), and (K). It is different in structure from the compounds of the formulae (F) and (G), in that it has a benzimidazolyl-1-yl group. As the group R2 of the formula (J), a heteroaryl group has been disclosed, but there is no specific disclosure of the benzimidazolyl-1-yl group, and there is no disclosure of the compound of the formula (I) of the present invention in Patent Document 16. Further, there is no description of a PI3K8 selective inhibitory action in any documents. [Chem. 1] (wherein R2 in the formulae (A-l) to (E-3) represents a difluoromethyl group or the like. R1 and R2 in the formula (F) are combined with each other to form an unsubstituted or substituted morpholino group, together with N to which they are bonded, X represents a bond or the like, and R3 represents an unsubstituted or substituted indolyl group. R2 in the formula (G) represents a substituted indol-4-yl group at the position 5 or 6. R3 in the formula (H) represents a difluoromethyl group or the like, and R6 represents a morpholino group which may be substituted, or the like. In the formula (J), Y1 and Y2 represent N, CH, or the like, X represents NR4CR6R7 or the like, R1 represents a heterocyclic group or the like, and R2 represents a heteroaryl group or the like. In the formula (K), X, Y, and Z represent N or CH, provided that at least two of X, Y, and Z represent N, R1 represents heteroaryl or the like, R2 represents a heterocycle or the like, Q represents a bond, azetidinylen-4-amino, or the like, T represents -C(O)-, -C(=S)-, or -S(0)2-, and R5 represents halogen or -0-S(0)2-R7. For the other symbols, reference may be made to the publication.) [0008] It has been reported that the compounds of the formula (L-l) (Patent Document 18), the formula (L-2) (Patent Document 19), the formula (L-3) (Patent Document 20), the formula (L-4) (Patent Document 21), and the formula (L-5) (Patent Document 22) described below have an anti-tumor activity. Further, in Non-Patent Document 2, it has been suggested that a secondary amine compound of the formula (M) has an Lck inhibitory action and an IL-2 production inhibitory action, and is applied for autoimmune diseases and rejection reaction in organ transplantation. However, the compound of the formula (I) of the present invention essentially has a difluoromethyl group, which is different in the structure from the compounds of the formulae (L-l), (L-2), and (M). It is also different in the structure of the group of R1 of the formula (I) from the compounds of the formulae (L-3) and (L-5). In addition, it is different in the structure of the substituent on a benzimidazole ring from the compound of the formulae (L-4). Further, there is no description of a PI3K5 selective inhibitory action in any literature. [Chem. 2] (in the formula (L-l), both of X and Y represent N, or one of X and Y represents N and the other represents CR7, and R6 represents H or Cj-6 alkyl; in the formula (L-2), both of X and Y represent N, or one of X and Y represents N and the other represents CR3, and R1 represents a morpholino group or the like; in the formula (L-3), X represents N or CH, R1 represents CHnF3.n (n is 1 or 2), and R2 represents morpholino which may be substituted, or the like; in the formula (L-4), X represents N or CH, and R1 represents halogen or a hydroxyl group; in the formula (L-5), X represents N or CH, R1 represents a morpholino group which may be substituted with 1 to 4 Ci.6 alkyl groups, and Y represents Cj.6 alkyl; and in the formula (M), R1 represents a morpholino group or the like. For the other symbols, reference may be made to the publication.) [0009] Furthermore, a quinazolin-4-one derivative (Patent Documents 23 to 25) has been reported as a PI3K8 selective inhibitor, and its usability in inflammation, immune diseases, or hematologic tumors (leukemia and the like) is indicated. As other PI3K5 selective inhibitors, a thiazolylurea derivative (Patent Document 26) has been reported together with its usability in inflammation, immune diseases, or the like. [0010] Furthermore, the invention relating to a triazine or pyrimidine derivative having a PI3K8 selective inhibitory action, which is an invention in the prior art by the present inventors, has been disclosed after the priority date of the present application (Patent Document 27). The compound of the present invention is different in the structure of the group R1 in the formula (I) from the compound disclosed in the prior application. Related Art Patent Documents [0011] [Patent Document 1] Pamphlet of International Publication WO 2008/032027 [Patent Document 2] Pamphlet of International Publication WO 2008/032077 [Patent Document 3] Pamphlet of International Publication WO 2008/032086 [Patent Document 4] Pamphlet of International Publication WO 2008/032028 [Patent Document 5] Pamphlet of International Publication WO 2008/032036 [Patent Document 6] Pamphlet of International Publication WO 2008/032041 [Patent Document 7] Pamphlet of International Publication WO 2008/032033 [Patent Document 8] Pamphlet of International Publication WO 2008/032060 [Patent Document 9] Pamphlet of International Publication WO 2008/032064 [Patent Document 10] Pamphlet of International Publication WO 2008/032072 [Patent Document 11] Pamphlet of International Publication WO 2008/032089 [Patent Document 12] Pamphlet of International Publication WO 2008/032091 [Patent Document 13] Pamphlet of International Publication WO 2007/042810 [Patent Document 14] Pamphlet of International Publication WO 2008/125839 [Patent Document 15] Specification of European Patent Application Publication No. 1864665 [Patent Document 16] Pamphlet of International Publication WO 2009/007751 [Patent Document 17] Pamphlet of International Publication WO 2009/120094 [Patent Document 18] Specification of European Patent Application Publication No. 1020462 [Patent Document 19] International Publication WO 00/43385 [Patent Document 20] Pamphlet of European Patent Application Publication No. 1389617 [Patent Document 21] Pamphlet of European Patent Application Publication No. 1557415 [Patent Document 22] Pamphlet of European Patent Application Publication No. 1741714 [Patent Document 23] Pamphlet of International Publication WO 01/81346 [Patent Document 24] Pamphlet of International Publication WO 03/035075 [Patent Document 25] Pamphlet of International Publication WO 2005/113556 [Patent Document 26] Pamphlet of International Publication WO 2008/000421 [Patent Document 27] Pamphlet of International Publication WO 2010/092962 Non-Patent Documents [0012] [Non-Patent Document 1] Journal of the National Cancer Institute, 2006, Vol. 98, p. 545-556 [Non-Patent Document 2] Bioorganic & Medicinal Chemistry Letters, 2006, Vol. 16, p. 5973-5977 Disclosure of Invention Problems to Be Solved by the Invention [0013] A pharmaceutical composition, for example, a pharmaceutical composition having a PI3K8 inhibitory action, in particular, a pharmaceutical composition for preventing and/or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumors, and a heterocyclic compound which is useful as an active ingredient of the pharmaceutical composition, are provided. Means for Solving the Problems [0014] The present inventors have extensively studied a PI3K8 selective inhibitory action and/or an IL-2 production inhibitory action and/or a B cell proliferation inhibitory action (including an activation inhibitory action), and as a result, they have found that a novel triazine or pyrimidine derivative has an excellent PI3K8 selective inhibitory action and/or IL-2 production inhibitory action and/or B cell proliferation inhibitory action (including an activation inhibitory action), and can be an agent for preventing and/or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor, thereby completing the present invention. [0015] That is, the present invention relates to a compound of the formula (I) or a salt thereof, and a pharmaceutical composition comprising the compound or a salt thereof and an excipient. [Chem. 3] (wherein A1, A2, and A3 are the same as or different from each other and are CH or N, provided that at least two of A1 to A3 are N, B's are the same as or different from each other and are CR3 or N, provided that at least three of four B's are CR3, R1 is -NH-lower alkylene-C(0)-OH or -L'-I^-Y, R2's are the same as or different from each other and are halogen, -OH, -O-lower alkyl, -CN, or lower alkyl which may be substituted with one or more substituents selected from the group consisting of halogen, -OH, -O-lower alkyl, and -CN, n is an integer of 0 to 8, R 's are the same as or different from each other and are H, -O-lower alkyl, cyano, -N(R4)2, -C(0)-OH, -C(0)-0-lower alkyl, -C(0)-N(R4)2, or lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -N(R4)2, -C(0)-OH, -C(0)-0-lower alkyl, -C(0)-N(R4)2, and halogen, R4's are the same as or different from each other and are H, or lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -CN, halogen, cycloalkyl, and phenyl, L1 is -lower alkynylene-, -NR5-, -NR5-S(0)2-, -NR5-C(0)-, -0-, -S-, or -S(0)m-, m's are the same as or different from each other and are 1 or 2, L2 is a bond, -ALK-X2-, -ALK-NR6-C(0)-, -ALK-NR6-C(0)-0-ALK-, -ALK-S(0)m-X1-, or -ALK-C(0)-X2-, ALK's are the same as or different from each other and are lower alkylene which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -CN, halogen, cycloalkyl, and phenyl, X1 is a bond, -NR6-, or -NR6-ALK-, X2's are the same as or different from each other and are a bond, -NR6-, -NR6-ALK-, -0-, -S-, -NR6-ALK-0-, -NR6-ALK-C(0)-NR6-, or -NR6-ALK-C(0)-, R5's are the same as or different from each other and are -R4, lower alkenyl, or cycloalkyl, R 's are the same as or different from each other and are H, cycloalkyl, phenyl, a non-aromatic heterocycle which may be substituted with lower alkyl, or lower alkyl which may be substituted with one or more substituents selected from the group consisting of -OH, -O-lower alkyl, -CN, halogen, -N(R4)2, cycloalkyl, phenyl, and a non-aromatic heterocycle, Y is lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -N(lower alkyl)2 and -C(0)-N(lower alkyl)2, cycloalkyl which may be substituted with one or more substituents selected from a Group Dl, aryl which may be substituted with one or more substituents selected from the Group Dl, an aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl, or a non-aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl, the Group Dl consists of: (1) halogen, (2) -O-R8, (3) -S-R8, (4)-CN, (5) -N02, (6) -NR4R7, in which R7 is -R8, -C(0)-R8, -C(0)-C(0)-N(R8)2, -C(0)-0-R8, and -S(0)2-R8, (7)-C(0)-R8, (8) -S(0)2-R8 and -S(0)2-N(R8)2, (9) -C(0)-0-R8, (10)-C(O)-N(R8)2, (11)-C(0)-C(0)-N(R8)2, (12) -0-C(0)-R8, -0-C(0)-NH-C(=NH)-NH2, and -0-C(0)-N(R8)2, (13) -L3-cycloalkyl, -L3-aryl, -L3-aromatic heterocycle, and -L3-non-aromatic heterocycle, in which the cycloalkyl, aryl, aromatic heterocycle, and non-aromatic heterocycle may be each substituted with one or more substituents selected from the group consisting of lower alkyl which may be substituted with one or more substituents selected from the group consisting of-O-R6, -CN, halogen, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, -S(0)2-lower alkyl, cycloalkyl, phenyl, and a non-aromatic heterocycle; oxo; cycloalkyl, aryl, aromatic heterocycle, and a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen; and the substituents of (1) to (12), (14) oxo, and (15) lower alkyl, -O-lower alkyl, and lower alkenyl, each of which may be substituted with one or more substituents selected from the substituents described in (1) to (14), L3's are the same as or different from each other and are -a bond, -0-, -S-, -NR5-, -NR5-S(0)2-, -NR5-C(0)-, -C(0)-NR5-, -S(0)m-, -ALK-, -0-ALK-, -ALK-0-, -O-ALK-O-, -S-ALK-, -ALK-S-, -ALK-S(0)m-, -S(0)m-ALK-5 -NR5-ALK-, -ALK-NR5-, -C(0)-NR5-ALK-, -C(0)-NR5-ALK-C(0)-, -C(0)-NR5-ALK-0-ALK-, -NR5-C(0)-ALK-, -NR5-C(0)-ALK-C(O)-, -NR5-C(0)-ALK-0-ALK-, -ALK-C(0)-NR5-, -ALK-NR5-C(0)-, -C(0)-0-, -ALK-C(0)-0-, -C(0)-0-ALK-, -C(0)-ALK-, -ALK-C(O)-, -NR5-C(0)-ALK-NR5-, or -C(O)-, R8's are the same as or different from each other and are H; cycloalkyl, phenyl, pyridyl, or a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen; -R9 or -ALK-L4-R9, in which R9 is lower alkyl which may be substituted with one or more substituents selected from the group consisting of -O-R6, -S-R6, -CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, -cycloalkyl, phenyl, and a non-aromatic heterocycle, and L4 is -C(O)-, -C(0)-NR5-, -NR5-, -NR5-S(0)2-, -NR5-C(0)-, -NR5-C(0)-0-, -0-, -S-, or -S(0)m-, provided that in a case where R1 has the following formula (II), all of B's are CH, W is NH or O, B is a bond or lower alkylene, and B is a bond or lower alkylene, [Chem. 4] R10 is -C(0)-(lower alkylene substituted with -NH-C(0)-0-lower alkyl)-S-lower alkyl, -C(0)-non-aromatic heterocycle, -C(0)-lower alkylene-NH-lower alkylene-(cycloalkyl which may be substituted with -OH), -C(0)-lower alkylene-NH-(cycloalkyl which may be substituted with a group selected from the group consisting of lower alkyl and -OH), -C(O)-lower alkylene-NH-non-aromatic heterocycle, -C(0)-lower alkylene-NH-(lower alkyl substituted with -OH), or -C(0)-(cycloalkyl substituted with one or more substituents selected from the group consisting of -NH2, -N(lower alkyl)2, and -NH-C(0)-0-lower alkyl), or R4 and R10 form a 4- to 8-membered monocyclic heterocyclic group containing 1 to 4 hetero atoms selected from O, S, and N, together with N to which they are bonded, and are further substituted with at least one substituent selected from a Group D2, in which the Group D2 consists of: (a) -0-(lower alkyl substituted with one or more substituents selected from the group consisting of -O-R6, -S-R6, -CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-O-R6, cycloalkyl, and a non-aromatic heterocycle), -0-(cycloalkyl, phenyl, pyridyl, or a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen), and -0-ALK-L4-R9, (b)-SR8, (c) -NO2, (d) -NRnR7, in which R7 is -R8, -C(0)-R8, -C(0)-C(0)-N(R8)2, -C(0)-0-R8, and -S(0)2-R8, and R11 is lower alkyl substituted with one or more substituents selected from the group consisting of -OH, -O-lower alkyl, -CN, halogen, cycloalkyl, and phenyl, (e) -C(0)-R8, (f) -S(0)2-R8 and -S(0)2-N(R8)2, (g) -C(0)-0-(lower alkyl substituted with one or more substituents selected from the group consisting of-O-R6, -S-R6, -CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, cycloalkyl, phenyl, and a non-aromatic heterocycle), -C(0)-0-(cycloalkyl, phenyl, pyridyl, or a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen), and -C(0)0-ALK-L4-R9, (h)-C(0)-N(R8)2, (i) -C(0)-C(0)-N(R8)2, (j) -0-C(0)-(lower alkyl substituted with one or more substituents selected from the group consisting of-O-R6, -S-R6, -CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, cycloalkyl, phenyl, and a non-aromatic heterocycle), -0-C(0)-(cycloalkyl, phenyl, pyridyl, or a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen), -0-C(0)-ALK-L4-R9, -0-C(0)-NH-C(=NH)-NH2, and -0-C(0)-N(R8)2, (k) lower alkyl substituted with one or more substituents selected from the group consisting of-CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, -S(0)2-lower alkyl, cycloalkyl, and phenyl, (1) cycloalkyl which may be substituted with one or more substituents selected from the groupconsisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen,(m) aryl which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen, (n) an aromatic heterocycle substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen, and (o) a non-aromatic heterocycle substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen.) Unless specified otherwise, in the case where the symbols of the chemical formulae in the present specification are also used in other chemical formulae, the same symbols denote the same meanings. [0016] Furthermore, the present invention relates to a pharmaceutical composition for preventing and/or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor, which comprises the compound of the formula (I) or a salt thereof as an active ingredient. Further, the pharmaceutical composition includes an agent for preventing and/or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor, which comprises the compound of the formula (I) or a salt thereof. In a certain embodiment, the present invention relates to an agent for preventing and/or treating rejection reactions in kidney, liver, and heart transplantations, in another embodiment, an agent for preventing and/or treating chronic rejection and acute rejection, and in still another embodiment, an agent for preventing and/or treating antibody-related rejection. Furthermore, the present invention relates to use of the compound of the formula (I) or a salt thereof in the manufacture of a pharmaceutical composition for preventing and/or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor, and use of the compound of the formula (I) or a salt thereof in preventing and/or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor, the compound of the formula (I) or a salt thereof for preventing and/or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor, and a method for preventing or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor, including administering to a subject an effective amount of the compound of the formula (I) or a salt thereof. Here, the "subject" is a human or any of other animals in need of prevention or treatment thereof, and in a certain embodiment, a human in need of prevention or treatment thereof. [0017] Furthermore, the present invention relates to a PI3K8 selective inhibitor and/or an IL-2 production inhibitor and/or a B cell proliferation inhibitor, each of which contains the compound of the formula (I) or a salt thereof. Effects of the Invention [0018] The compound of the formula (I) has a PI3K8 selective inhibitory action and/or an IL-2 production inhibitory action and/or a B cell proliferation inhibitory action (including an activation inhibitory action), and can therefore be used as an agent for preventing or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor. Embodiments for Carrying Out the Invention [0019] Hereinbelow, the present invention will be described in detail. [0020] The "lower alkyl" is linear or branched alkyl having 1 to 6 carbon atoms (which is hereinafter simply referred to as Ci-6), and examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, and the like. In another embodiment, the lower alkyl is CM alkyl, in still another embodiment, methyl, ethyl, or tert-butyl, and in a further still other embodiment, methyl. [0021] The "lower alkenyl" is linear or branched C2-6 alkenyl, and examples thereof include vinyl, propenyl, butenyl, pentenyl, 1-methylvinyl, 1-methyl-2-propenyl, 1,3-butadienyl, 1,3-pentadienyl, and the like. In another embodiment, the lower alkenyl is C2-4 alkenyl, and in still another embodiment, propenyl. [0022] The "lower alkylene" is a divalent group formed by the removal of any hydrogen atom of the "lower alkyl". Accordingly, the "C1-6 alkylene" is linear or branched alkylene having 1 to 6 carbon atoms, and examples thereof include methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, methylmethylene, dimethylmethylene, ethylmethylene, methylethylene, dimethylethylene, ethylethylene, and the like. In another embodiment, the lower alkylene is methylene, ethylene, and in still another embodiment, methylene. [0023] The "lower alkenylene" is linear or branched C2-6 alkenylene, and examples thereof include vinylene, ethylidene, propenylene, butenylene, pentenylene, hexenylene, 1,3-butadienylene, 1,3-pentadienylene, and the like. In another embodiment, the lower alkenylene is C2-4 alkenylene, and in still another embodiment, propenylene. [0024] The "lower alkynylene" is linear or branched C2-6 alkynylene, and examples thereof include ethynylene, propynylene, butynylene, pentynylene, hexynylene, 1,3-butadiynylene, 1,3-pentadiynylene, and the like. In another embodiment, the lower alkynylene is C2-4 alkynylene, and in still another embodiment, propynylene. [0025] The "halogen" is F, CI, Br, or I, in another embodiment, F, and in still another embodiment, CI. [0026] The "cycloalkyl" is C3.10 saturated hydrocarbon ring group, which may have a bridge and may be combined with a non-aromatic heterocyclic group to form a spiro ring. Specific examples thereof include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclohexenyl, cyclooctyl, bicyclo[3.3.0]octane, hexahydro-l'H-spiro-l,3-dioxane-2,2'-pentalene, l,4-dioxaspiro[4.5]decane, bicyclo[2.2.2]octyl, adamantyl, azaspiro[5.5]undecanyl, octahydrocyclopenta[c]pyrrole, indanyl, and the like. In another embodiment, the cycloalkyl is cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, octahydropentalene, bicyclo[2.2.2]octyl, or adamantyl, in still another embodiment, C3.8 cycloalkyl, in further still another embodiment, C3.6 cycloalkyl, in further still another embodiment, cyclohexyl, in further still another embodiment, octahydropentalene, and in further still another embodiment, adamantyl. [0027] The "aryl" is C6-14 monocyclic to tricyclic aromatic hydrocarbon ring group, and examples thereof include phenyl, naphthyl, and the like. In another embodiment, the aryl is phenyl. [0028] The "aromatic heterocycle" is an aromatic heterocycle having 5 to 6 ring members, containing at least one hetero atom selected from O, N, and S as a ring-constituting atom, and may be fused with a benzene ring or an aromatic heterocycle. Examples thereof include pyridyl, pyrrolyl, pyrazinyl, pyrimidinyl, pyridazinyl, imidazolyl, triazolyl, triazinyl, tetrazolyl, thiazolyl, pyrazolyl, isothiazolyl, oxazolyl, isooxazolyl, thiadiazolyl, oxadiazolyl, thienyl, furyl, indolyl, isoindolyl, benzoimidazolyl, indazolyl, quinolyl, isoquinolyl, quinazolinyl, quinoxalinyl, phthalazinyl, benzothiazolyl, benzoisothiazolyl, benzothiadiazolyl, benzoxazolyl, benzoisoxazolyl, benzofuranyl, benzothienyl, carbazolyl, dibenzo[b,d]furanyl, dibenzo[b,d]thienyl, thienopyridyl, thienopyrimidinyl, thienopyrazyl, 1,4-benzodioxin-2-yl, [l,2,4]triazolo[4,3-a]pyridyl, imidazo[l,2-a]pyridyl, and the like. In another embodiment, the aromatic heterocycle is imidazolyl, pyridyl, pyrazinyl, indolyl, indazolyl, benzoimidazolyl, or benzothiazolyl. [0029] The "non-aromatic heterocycle" is a non-aromatic heterocycle having 4 to 8 ring members, containing at least one hetero atom selected from O, N, and S as a ring-constituting atom, which may have unsaturated bonds in a part of the ring and may be bridged. The non- aromatic heterocycle may be fused with a benzene ring or an aromatic heterocycle. Further, the sulfur atom that is a ring-constituting atom may be oxidized. Examples of the non-aromatic heterocycle include azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, azepanyl, diazepanyl, morpholinyl, thiomorpholinyl, quinuclidinyl, 1,1-dioxidethiomorpholinyl, tetrahydropyridinyl, oxetanyl, tetrahydrofuranyl, tetrahydropyranyl, tetrahydrothienyl, 4,5-dihydrothiazolyl, dioxolanyl, dioxanyl, tetrahydrothiopyranyl, tetrahydroisoquinolyl, oxazolidinyl, tropane, 3,9-diazaspiro[5.5]undecanyl, 2,8-diazaspiro[4.5]decanyl, octahydropyrrolo[l,2-a]pyrazyl, 5,6,7,8-tetrahydro-l,7-naphthalidyl, 3,4-dihydro-2H-l,4-benzoxazinyl, 1,3-benzodioxolyl, chromenyl, 1,4-benzothiazinyl, 4,5-dihydro-l,3-thiazolyl, and the like. In another embodiment, the non-aromatic heterocycle is azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, morpholinyl, tetrahydrofuranyl, tetrahydropyranyl, or azepanyl, in still another embodiment, pyrrolidinyl, piperidinyl, tetrahydropyranyl, or azepanyl, in further still another embodiment, piperidinyl, and in further still another embodiment, pyrrolidinyl. [0030] The "cyclic amino" is a non-aromatic heterocyclic group having a nitrogen atom-containing group and has a bonding position on the nitrogen atom, among the above "non-aromatic heterocycles" and may form a spiro ring, and specific examples thereof include pyrrolidin-1-yl, piperidin-1-yl, azepan-1-yl, piperazin-1-yl, l,3-oxazolidin-2-one, morpholin-4-yl, thiomorpholin-4-yl, l,l-dioxidethiomorpholin-4-yl, 2-oxa-6-azaspiro[3.3]hept-6-yl, 1-oxa-3-azaspiro[4.5]decan-2-one, 2,5-diazabicyclo[2.2.1]heptane, 2-oxa-5-azaspiro[3.4]octane, 2-oxa-5-azabicyclo[2.2.1]heptane, and the like. In another embodiment, the cyclic amino is pyrrolidin-1-yl. [0031] Furthermore, the monocyclic heterocyclic group in the expression "R10 and R4 form a 4- to 8-membered monocyclic heterocyclic group containing 1 to 4 hetero atoms selected from O, S, and N, together with N to which they are bonded" is a 4- to 8-membered monocyclic group containing 1 to 4 hetero atoms selected from O, S, and N in the "aromatic heterocycle" and the "cyclic amino" above. [0032] In the present specification, the expression "which may be substituted" means non-substitution or substitution with 1 to 5 substituents. In a certain embodiment, it is unsubstitution or substitutions with 1 to 3 substituents, in another embodiment, unsubstitution or substitution with 1 substituent, and in still another embodiment, unsubstitution. Further, in a case of having a plurality of substituents, the substituents may be the same as or different from each other. [0033] In a certain embodiment, the Group Dl consists of: (1) halogen, (2)-OH, (3) -O-lower alkyl, (4) -CN, (5) -N02, (6) -NR4aR7, in which R4a is H or lower alkyl, R7 is lower alkyl which may be substituted with one or more substituents selected from the group consisting of halogen, -OH, -O-lower alkyl, and aryl, -C(0)-lower alkyl, -C(0)-lower alkylene-N(lower alkyl)2, lower alkenyl, -C(0)-lower alkylene-NH-(lower alkyl substituted with cycloalkyl), -C(0)-lower alkylene-NH-(cycloalkyl which may be substituted with lower alkyl), -C(0)0-lower alkyl or H, (7) -C(0)-lower alkyl, (8) -C(0)-lower alkylene-N(R4)2, (9) -C(0)0-lower alkyl, (10) -C(O) OH, (11)-C(0)-N(R4)2, (12) -0-C(0)-NH-C(=NH)-NH2, (13) -L5-cycloalkyl, -L5-aryl, -L5-aromatic heterocycle, and -L5-non-aromatic heterocycle, in which the cycloalkyl, aryl, aromatic heterocycle, and non-aromatic heterocycle may be each substituted with one or more substituents selected from the group consisting of lower alkyl which may be substituted with one or more substituents selected from the group consisting of -OH, halogen, -O-lower alkyl, and a non-aromatic heterocycle, -OH, -O-lower alkyl, -NH2, halogen, -C(0)0-lower alkyl, -C(0)-lower alkyl, oxo, -NH-S(0)2-lower alkyl, -NH-S(0)2-cycloalkyl, -NH-C(0)-lower alkyl, -NR4-C(0)-0-(lower alkyl which may be substituted with -OH), -S(0)2-lower alkyl, -NH-(lower alkyl which may be substituted with -OH), cycloalkyl which may be substituted with -OH, and a non-aromatic heterocycle, in which L5's are the same as or different from each other and are a bond, -0-, -lower alkylene, -O-lower alkylene, -O-lower alkylene-O-, -C(0)-NH-, -NH-C(O)-, -C(0)-lower alkylene-, or -C(O)-; in another embodiment, the cycloalkyl may be substituted with one or more substituents selected from the group consisting of lower alkyl which may be substituted with one or more substituents selected from the group consisting of halogen, -OH, and -O-lower alkyl, halogen, -OH, -O-lower alkyl, -NH-lower alkyl-OH, -NH2, -NH-C(0)-0-lower alkyl, -NH-lower alkyl, and -C(0)-0-lower alkyl; the aryl may be substituted with one or more substituents selected from the group consisting of lower alkyl, halogen, -O-lower alkyl, and -C(0)-0-lower alkyl; the aromatic heterocycle may be substituted with one or more substituents selected from the group consisting of lower alkyl and -NH2; and the non-aromatic heterocycle may be substituted with one or more substituents selected from the group consisting of lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, halogen, -O-lower alkyl, and a non-aromatic heterocycle, -NH2, halogen, -C(0)-0-lower alkyl, -C(0)-lower alkyl, oxo, -NH-S(0)2-lower alkyl, -NH-S(0)2-cycloalkyl, -NH-C(0)-lower alkyl, -NR4-C(0)-0-(lower alkyl which may be substituted with -OH), -S(0)2-lower alkyl, -NH-(lower alkyl substituted with -OH), cycloalkyl which may be substituted with -OH, and a non-aromatic heterocycle, (14) oxo, and (15) lower alkyl, -O-lower alkyl, and lower alkenyl, each of which may be substituted with one or more substituents selected from the substituents described in (1) to (14) above. [0034] In another embodiment, the Group Dl consists of: (1) halogen, (2)-OH, (3) -O-lower alkyl, (4) -NR4aR7, in which R4a represents H or lower alkyl, R7 represents lower alkyl which may be substituted with -OH, -C(0)-lower alkylene-N(lower alkyl)2, -C(0)-lower alkylene-NH-(lower alkyl substituted with cycloalkyl), -C(0)-(cycloalkyl substituted with -NH2), -C(0)-lower alkylene-NH-tetrahydropyran, -C(0)-lower alkylene-N(lower alkyl)-(cycloalkyl which may be substituted with lower alkyl) or -C(0)-lower alkylene-NH-(cycloalkyl which may be substituted with lower alkyl), (5) -C(0)-lower alkylene-N(R4)2, (6) -C(0)0-lower alkyl, (7) -L5-(aryl which may be substituted with one or more substituents selected from the group consisting of lower alkyl, halogen, and -O-lower alkyl), (8)-L5-(non-aromatic heterocycle which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -NH-C(0)-0-lower alkyl, -NH-C(0)-lower alkyl, -C(0)-0-lower alkyl, -C(0)-lower alkyl, -S(0)2-lower alkyl, oxo, and -NH-lower alkyl), (9)-L5-(cycloalkyl which may be substituted with one or more substituents selected from the group consisting of lower alkyl which may be substituted with one or more groups selected from the group consisting of halogen and-OH, halogen, -OH, -O-lower alkyl, and -C(0)0-lower alkyl), and (10) lower alkyl which may be each substituted with one or more substituents selected from the substituents described in (1) to (9) above. [0035] In still another embodiment, the Group Dl consists of: (l)-OH, (2) -O-lower alkyl, (3) -NR4aR7, in which R4a represents H or lower alkyl, R7 represents lower alkyl which may be substituted with -OH, -C(0)-(cycloalkyl substituted with -NH2), -C(0)-lower alkylene-NH-tetrahydropyran, -C(0)-lower alkylene-N(lower alkyl)-(cycloalkyl which may be substituted with lower alkyl), or -C(0)-lower alkylene-NH-(cycloalkyl which may be substituted with lower alkyl), (4) -L5a-(non-aromatic heterocycle which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -NH-C(0)-0-lower alkyl, -NH-C(0)-lower alkyl, -C(0)-0-lower alkyl, -C(0)-lower alkyl, and oxo), in which L5a represents a bond, -C(0)-lower alkylene-, or -C(O)-, and (5) -L5b-(cycloalkyl which may be substituted with one or more substituents selected from the group consisting of lower alkyl which may be substituted with -OH, halogen, -OH, and -O-lower alkyl), in which L5b represents a bond or -C(O)-. [0036] In further still another embodiment, the Group Dl consists of: (1) -L5a-(non-aromatic heterocycle which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -NH-C(0)-0-lower alkyl, -C(0)0-lower alkyl, -C(0)-lower alkyl, and oxo), in which L5a represents a bond, -C(O)-lower alkylene-, or -C(O)-, and (2) -C(0)-(cycloalkyl which may be substituted with one or more substituents selected from the group consisting of lower alkyl which may be substituted with -OH, -OH, and-O-lower alkyl). [0037] Certain embodiments of the compound of the formula (I) of the present invention are shown below. (1) In a certain embodiment of A , A and A , any one of A , A and A is CH, in another embodiment, A1 and A3 are N and A2 is CH, and in still another embodiment, A2 and A3 are N and A1 is CH. (2) In a certain embodiment of B, all of B's are CR , in which R is H, lower alkyl which may be substituted with halogen, or -O-lower alkyl, in another embodiment, R3 is H or lower alkyl, in still another embodiment, R3 is lower alkyl, in further still another embodiment, R3 is H, in further still another embodiment, one of B's is N and the others are CH, and in further still another embodiment, all of B's are CH. (3) In a certain embodiment of R1, R1 is -L'-I^-Y. (4) In a certain embodiment of L1, L1 is -NR5-, -NR5-S(0)2-, -NR5-C(0)-, or -0-, in another embodiment, L1 is -NH-, -N(lower alkyl)-, or -0-, in still another embodiment, -NH-or -0-, in further still another embodiment, -NH-, and in further still another embodiment, -O- (5) In a certain embodiment, L2 is a bond, -ALK-, -ALK-S-, -ALK-S(0)m-X1-, or -ALK-C(0)-X2-, in which X1 is a bond or -NR6-, X2 is a bond, -NR6-, -NR6-ALK-, or -0-, ALK is lower alkylene, and R is H or lower alkyl, in another embodiment, L is a bond, lower alkylene, or -lower alkylene-C(0)NH-, in still another embodiment, a bond or lower alkylene, in further still another embodiment, a bond, in further still another embodiment, lower alkylene, and in further still another embodiment, methylene. (6) In a certain embodiment, Y is cycloalkyl which may be substituted with one or more substituents selected from the Group Dl, aryl which may be substituted with one or more substituents selected from the Group Dl, an aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl, or a non-aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl, in another embodiment, cycloalkyl which may be substituted with one or more substituents selected from the Group Dl or a non-aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl, in still another embodiment, cycloalkyl which may be substituted with one or more substituents selected from the Group Dl, in further still another embodiment, a non-aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl, in further still another embodiment, cyclohexyl or cyclic amino, in further still another embodiment, cyclohexyl, in further still another embodiment, cyclic amino, in further still another embodiment, piperidinyl, pyrrolidinyl, or azetidinyl, and in further still another embodiment, pyrrolidinyl or azetidinyl. (7) In a certain embodiment, n is an integer of 0 or 1 to 2, and in another embodiment, 0. (8) In a certain embodiment, R 's are the same as or different from each other and are lower alkyl which may be substituted with halogen. (9) The compound or a salt thereof, which is a combination of any two or more of the embodiments of (1) to (8) as described above. [0038] The compound or a salt thereof, which is a combination of any two or more of the embodiments of (1) to (8) as described above, is also included in the present invention, as described in (9) above, and the specific examples thereof also include the following embodiments. (10)The compound or a salt thereof, wherein R1 is -NH-lower alkylene-C(0)-OH or -L!-L2-Y, L1 is -lower alkynylene-, -NR5-, -NR5-S(0)2-, -NR5-C(0)-, -0-, -S-, or -S(0)m-, rn is 1 or 2, L2 is a bond, -ALK-X2-, -ALK-NR6-C(0)-, -ALK-NR6-C(0)-0-ALK-, -ALK-S(0)m-X -, or -ALK-C(0)-X -, ALK's are the same as or different from each other and are lower alkylene which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -CN, halogen, and cycloalkyl, X1 is a bond, -NR6-, or -NR6-ALK-, X2's are the same as or different from each other and are a bond, -NR6-, -NR6-ALK-, -0-, -S-, -NR6-ALK-0-, -NR6-ALK-C(0)-NR6-, or -NR6-ALK-C(0)-, R4's are the same as or different from each other and are H, or lower alkyl which may be substituted with one or more substituents selected from the group consisting of -OH, -O-lower alkyl, -CN, halogen, and cycloalkyl, R5's are the same as or different from each other and are -R4, lower alkenyl, or cycloalkyl, R6,s are the same as or different from each other and are H, cycloalkyl, a non-aromatic heterocycle which may be substituted with lower alkyl, or lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -CN, halogen, -N(R4)2, cycloalkyl, and a non-aromatic heterocycle, Y is lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -N(lower alkyl)2 and -C(0)-N(lower alkyl)2, cycloalkyl which may be substituted with one or more substituents selected from the Group Dl, or a non-aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl, provided that L2 is -ALK-X2a-, -ALK-NR6-C(0)-, -ALK-NR6-C(0)-0-ALK-, -ALK-S(0)m-X1-, or -ALK-C(0)-X2-, in which in a case where X2a is -NR6-, -NR6-ALK-, -0-, -S-, -NR6-ALK-0-, -NR6-ALK-C(0)-NR6-, or -NR6-ALK-C(0)-, Y is aryl which may be substituted with one or more substituents selected from the Group Dl or an aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl. (11) The compound or a salt thereof as described in (10), wherein R1 is -I^-I^-Y, L1 is -NR5-, -NR5-S(0)2-, -NR5-C(0)-, or -0-, in which R5 is H or lower alkyl, L2 is a bond, -ALK-, -ALK-S-, -ALK-S(0)m-X1-, or -ALK-C(0)-X2-, in which X1 is a bond or -NR6-, X2 is a bond, -NR6-, -NR6-ALK-, or -0-, ALK is lower alkylene, R6 is H or lower alkyl, and Y is cycloalkyl which may be substituted with one or more substituents selected from the Group Dl, or a non-aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl. (12) The compound or a salt thereof as described in (11), wherein -L!-L2- is -NH- or -0-. (13) The compound or a salt thereof as described in (12), wherein B's are all CH and n is 0. (14) The compound or a salt thereof as described in (13), wherein A1 and A3 are N and A2 is CH. (15) The compound or a salt thereof as described in (13), wherein A2 and A3 are N and A1 is CH. [0039] Examples of the specific compounds included in the compound of the formula (I) or a salt thereof include the following compounds: methyl {(3S)-l-[trans-4-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl} oxy)cyclohexyl] -2-oxopyrrolidin-3 -y 1} carbamate, methyl {(3R)-1 -[trans-4-({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl}oxy)cyclohexyl]-2-oxopyrrolidin-3-yl}carbamate, ethyl {(3 R)-1 -[trans-4-( {6-[2-(difiuoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} oxy )cyclohexyl] -2-oxopyrrolidin-3 -yl} carbamate, [(3 S)-3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] [(2R)-tetrahydrofuran-2-yl]methanone, [(3 S)-3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] (tetrahydro-2H-pyran-4-yl)methanone, methyl {(3S)-1 -[trans-4-({4-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-6-(morpholin-4-yl)pyrimidin-2-yl} amino)cyclohexyl] -2-oxopyrrolidin-3 -yl} carbamate, methyl {(3R)-1 -[trans-4-({4-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-6-(morpholin-4-yl)pyrimidin-2-yl} amino)cyclohexyl] -2-oxopyrrolidin-3 -yl} carbamate, methyl {(3R)-1 -[trans-4-({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)cy clohexy 1] -2-oxopyrrolidin-3 -yl} carbamate, 1 -[(3 S)-3 -({6-[2-(difluoromethyl)-l H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] -2-(tetrahydrofuran-2-yl)ethanone, 1 -[(3 S)-3 -( { 6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] -2-(tetrahydro-2H-pyran-4-yl)ethanone, l-[3-({6-[2-(difluorometiiyl)-lH-benzimidazol-l-yl]-2-(morpholm-4-yl)pyrirnidin-4-yl} oxy)azetidin-1 -yl] -2-(tetrahydrofuran-2-yl)ethanone, methyl 4- {[(3 S)-3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] carbonyl }piperidine-1 -carboxylate, [(3 S)-3 -({ 6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} oxy)pyrrolidin-1 -yl](tetrahydrofuran-3-yl)methanone, 4- {[(3 S)-3 -({6- [2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} oxy)pyrrolidin-1 -yl] carbonyl} -1 -methylpyrrolidin-2-one, 2-( 1 -acetylpiperidin-4-yl)-1 -[(3 S)-3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] ethanone, [(3 S)-3 -({6- [2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] (tetrahydrofuran-3-yl)methanone, 4- {[(3 S)-3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yljcarbonyl} -1 -methylpyrrolidin-2-one, l-[(3S)-3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2- (morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] -2-(piperidin-1 -yl)ethanone, (5S)-5-{[3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl} oxy)azetidin-1 -yljcarbonyl} pyrrolidin-2-one, (5S)-5-{[3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-y l)pyrimidin-4-yl} amino)azetidin-1 -yl] carbonyl} pyrrolidin-2-one, 2-(l -acetylpiperidin-4-yl)-1 -[3-({6-[2-(difluoromethyl)-l H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl}amino)azetidin-l-yl]ethanone, [3-( {6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)azetidin-1 -yl] (tetrahydrofuran-3 -yl)methanone, 4- {[3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)azetidin-1 -yl] carbonyl} -1 -methylpyrrolidin-2-one, [(3S)-3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl}amino)pyrrolidin-l-yl][cis-4-(hydroxymethyl)cyclohexyl]methanone, and [(3S)-3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl}amino)pyrrolidin-l-yl][trans-4-(hydroxymethyl)cyclohexyl]methanone, and salts thereof. [0040] The compound of the formula (I) may exist in the form of tautomers or geometrical isomers depending on the kind of substituents. In the present specification, the compound of the formula (I) shall be described in only one form of isomer, yet the present invention includes other isomers, isolated forms of the isomers, or a mixture thereof. In addition, the compound of the formula (I) may have asymmetric carbon atoms or axial asymmetry in some cases, and correspondingly, it may exist in the form of optical isomers based thereon. The present invention includes both an isolated form of the optical isomers of the compound of the formula (I) or a mixture thereof. [0041] Moreover, the present invention also includes a pharmaceutically acceptable prodrug of the compound represented by the formula (I). The pharmaceutically acceptable prodrug is a compound having a group that can be converted into an amino group, a hydroxyl group, a carboxyl group, or the like through solvolysis or under physiological conditions. Examples of the group forming the prodrug include the groups described in Prog. Med., 5, 2157-2161 (1985) and "Pharmaceutical Research and Development" (Hirokawa Publishing Company, 1990), Vol. 7, Molecular Design, 163-198. [0042] Furthermore, the salt of the compound of the formula (I) may form an acid addition salt or a salt with a base depending on the kind of substituents, and such salts are included in the present invention as long as they are pharmaceutically acceptable salts. Specific examples thereof include acid addition salts with inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, and phosphoric acid, and with organic acids such as formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, fumaric acid, maleic acid, lactic acid, malic acid, mandelic acid, tartaric acid, dibenzoyltartaric acid, ditoluoyltartaric acid, citric acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, aspartic acid, and glutamic acid, and salts with inorganic bases such as sodium, potassium, magnesium, calcium, and aluminum, or organic bases such as methylamine, ethylamine, ethanolamine, lysine, and ornithine, salts with various amino acids such as acetylleucine, and amino acid derivatives, as well as ammonium salts. [0043] In addition, the present invention also includes various hydrates or solvates, and polymorphic crystalline substances of the compound of the formula (I) and pharmaceutically acceptable salts thereof. In addition, the present invention also includes compounds labeled with various radioactive or non-radioactive isotopes. [0044] The "PI3K8 selective inhibitor" means an inhibitor exhibiting a potent activity, in which the inhibitory activity of PI3K5 is 10-times or more, in another embodiment, 30-times or more, and in still another embodiment, 100-times or more than the inhibitory activity of PDKoc in terms of the IC50 value. [0045] (Preparation Methods) The compound of the formula (I) and a pharmaceutically acceptable salt thereof can be prepared by applying various known synthesis methods on the basis of characteristics derived from their skeletal structure or the type of their substituents. During the preparation, replacement of the relevant functional group with a suitable protective group (a group that can be easily converted into the relevant functional group) at the stage from starting material to an intermediate may be effective depending on the type of the functional group in the production technology in some cases. Examples of such the functional group include an amino group, a hydroxyl group, and a carboxyl group, and such the protective group for such a functional group may include, for example, the protective groups described in Greene and Wuts, "Protective Groups in Organic Synthesis (3rd edition, 1999)", which may be selected and used as appropriate, depending on reaction conditions. In such a method, after introduction of the protective group and a subsequent reaction, the protective group may be removed, if necessary to obtain a desired compound. In addition, the prodrug of the compound of the formula (I) can be prepared by introducing a specific group at the stage from a starting material to an intermediate, or by carrying out the reaction using the obtained compound of the formula (I), as in the case of the above-mentioned protective group. The reaction can be carried out using methods known to those skilled in the art, such as ordinary esterification, amidation, dehydration, and the like. Hereinbelow, the representative preparation methods for the compound of the formula (I) will be described. Each of the production processes may also be carried out with reference to the References appended in the present description. Further, the preparation methods of the present invention are not limited to the examples as shown below. [0046] (Production Process 1) [Chem. 5] (wherein X represents a leaving group, R21 represents -NH-lower alkylene-C(0)-OH or -L'-L2-Y, and L1 represents -NR5-, -NR5-S(0)2-, -NR5-C(0)-, -0-, -S-, or -S(0)m-. The same shall apply hereinafter.) [0047] The compound (1-1) of the present invention can be obtained by the ipso substitution reaction of the compound (1) with, for example, -L!-L2-Y. Examples of the leaving group X include halogen, methylsulfinyl, methylsulfonyl groups, and the like. The present reaction is carried out by using the compound (1) and, for example, a compound -L -L - Y in equivalent amounts, or either thereof in an excess amount, and stirring a mixture thereof in a solvent which is inert to the reaction, or in the absence of a solvent, in a range of from cooling to heating and refluxing, preferably at 0°C to 100°C, usually for 0.1 hours to 5 days. Examples of the solvent used herein are not particularly limited, but include aromatic hydrocarbons such as benzene, toluene, xylene, and the like, ethers such as diethyl ether, tetrahydrofuran, dioxane, dimethoxyethane, and the like, halogenated hydrocarbons such as dichloromethane, 1,2-dichloroethane, chloroform, and the like, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, ethyl acetate, acetonitrile, and a mixture thereof. It is preferable in some cases for the smooth progress of the reaction to use organic bases such as triethylamine, N,N-diisopropylethylamine, N-methylmorpholine, and the like, or inorganic bases such as potassium carbonate, sodium carbonate, cesium carbonate, potassium hydroxide, and the like. It may be advantageous in some cases for the smooth progress of the reaction to carry out the reaction by heating the reaction mixture by microwave irradiation. [Documents] S. R. Sandler and W. Karo, "Organic Functional Group Preparations", 2nd edition, Vol. 1, Academic Press Inc., 1991 "Jikken Kagaku Koza (Courses in Experimental Chemistry) (5th Edition) (Vol. 14)", edited by The Chemical Society of Japan, Maruzen, 2005 [0048] (Production Process 2) [Chem. 6] [0049] The compound of the formula (1-2) can be obtained by the reaction of a compound (2) and a compound (3). The reaction conditions are the same as in the Production Process 1. [0050] (Production Process 3) [Chem. 7] (wherein L12 represents -lower alkynylene.) [0051] The compound (1-3) of the present invention can be obtained by a Sonogashira coupling reaction of a compound (4) and a terminal alkyne derivative. Examples of the leaving group X include halogen, and the like. The present reaction is carried out by using the compound (4) and the terminal alkyne derivative in equivalent amounts, or either thereof in an excess amount, and stirring a mixture thereof in a solvent which is inert to the reaction, under the temperature condition ranging from room temperature to heating and refluxing, usually for 0.1 hours to 5 days, in the presence of a base and a palladium catalyst. The present reaction is preferably carried out under inert gas atmosphere. Examples of the solvent used herein are not particularly limited, but include aromatic hydrocarbons such as benzene, toluene, xylene, and the like, ethers such as diethyl ether, tetrahydrofuran, dioxane, dimethoxyethane, and the like, halogenated hydrocarbons such as dichloromethane, 1,2-dichloroethane, chloroform, and the like, alcohols such as methanol, ethanol, 2-propanol, butanol, and the like, N,N-dimethylformamide, dimethylsulfoxide, and a mixed solvent thereof. As the base, inorganic bases such as potassium carbonate, sodium carbonate, cesium carbonate, potassium hydroxide, and the like are preferable. As the palladium catalyst, tetrakis(triphenylphosphine)palladium, dichlorobis(triphenylphosphine)palladium, palladium-1,1 '-bis(diphenylphosphino)ferrocene chloride, and the like are preferred. Further, it may be advantageous in some cases for the smooth progress of the reaction to heat the reaction mixture by microwave irradiation. [Documents] "Metal-Catalyzed Cross-Coupling Reactions", edited by A. d. Meijere and F. Diederich, Vol. 1, VCH Publishers Inc., 1997 "Jikken Kagaku Koza (Courses in Experimental Chemistry) (5 Edition)", edited by The Chemical Society of Japan, Vol. 13 (2005) (Maruzen) [0052] Various substituents on R1 in the compound of the formula (I) can be easily converted into other functional groups by using the compound of the formula (I) as a starting material by means of the reactions described in Examples as described later, the reactions apparent to a person skilled in the art, or modified methods thereof. For example, the steps that can be usually employed by a person skilled in the art, such as O-alkylation, N-alkylation, oxidation, reduction, reductive alkylation, ring formation, hydrolysis, amidation, acylation, deprotection, epoxylation, and the like can be arbitrarily combined and performed. [0053](Preparation of Starting Compound) In the preparation method above, the starting compound can be prepared by using any of, for example, the methods below, the methods described in Preparation Examples as described later, known methods, or modified methods thereof. [0054] (Starting Material Synthesis 1) [Chem. 8] [0055] The present production process is a method for preparing a compound (9), in which X is -S(0)m-methyl in (1) which is the starting compound in Production Process 1. [0056] A compound (7) can be obtained by the reaction of a compound (5) with a compound (6). The reaction condition is the same as in Production Process 1. [0057] A compound (8) can be obtained by the reaction of the compound (7) with the compound (3). The reaction condition is the same as in Production Process 1. [0058] A compound (9) can be obtained by the oxidation reaction of the compound (8). The present reaction can be carried out by using the compound (9) in an equivalent amount or an excess amount, in a range of from cooling to heating. As the solvent, solvents such as aromatic hydrocarbons and halogenated hydrocarbons may be used singly or in a mixture of two or more kinds thereof. Examples of the oxidant include m-chloroperbenzoic acid, peracetic acid, and a hydrogen peroxide solution. [0059] (Starting Material Synthesis 2) [Chem. 9] [0060] The present production process is a method for preparing a compound (13), in which X is -S(0)m-methyl and R1 is R21, in (2) which is the starting compound in Production Process 2. [0061] A compound (11) can be obtained by the reaction of the compound (10) with the compound (6). The reaction conditions are the same as in Production Process 1. [0062] A compound (12) can be obtained by the ipso substitution reaction of the compound (11) with, for example, -L'-IAY. The reaction conditions are the same as in Production Process 1. [0063] A compound (13) can be obtained by the oxidation reaction of the compound (12). The reaction conditions are the same as in the oxidation reaction described in Starting Material Synthesis 1. [0064] Other starting compounds (1), (2), and (4) can be prepared by, for example, the methods described in the following documents: WO2002/088112, EP1389617, WO2008/032033, WO2008/032036, WO2008/032041, or WO2008/032060. [0065] The compounds of the formula (I) can be isolated and purified as their free compounds, pharmaceutically acceptable salts, hydrates, solvates, or polymorphic crystalline substances thereof. The pharmaceutically acceptable salts of the compound of the formula (I) can be prepared by carrying out the treatment of a conventional salt forming reaction. Isolation and purification are carried out by employing ordinary chemical operations such as extraction, fractional crystallization, various types of fractional chromatography, and the like. Various isomers can be prepared by selecting an appropriate starting compound or separated by using the difference in the physicochemical properties between the isomers. For example, the optical isomers can be obtained by means of a general method for designing optical resolution of racemates (for example, fractional crystallization for inducing diastereomer salts with optically active bases or acids, chromatography using a chiral column or the like, and others), and further, the isomers can also be prepared from an appropriate optically active starting compound. [0066] The pharmacological activity of the compound of the formula (I) was confirmed by the tests shown below. 1. PI3K5 Enzyme Inhibitory Activity For the experiment, a PI3-Kinase HTRJ Assay kit (Millipore Corporation, Catalogue No. 33-016) and a human PI3K8 enzyme (Millipore Corporation, Catalogue No. 14-604) were used. The measurement method was in accordance with the appended instructions. The overview thereof is as follows. PI3K8 (10 ng/well), phosphatidylinositol-4,5-bisphosphate (10 uM), ATP (30 uM), and the test compound were mixed in a 384-well plate (total 20 uL), and incubated at room temperature for 30 minutes. EDTA and biotinylated phosphatidylinositol-3,4,5-triphosphate were added thereto to stop the reaction. Thereafter, a Europium labeled anti-GST antibody, a GST bond GRP1 PH domain, and streptavidin-APC were added thereto, followed by incubation overnight. An HTRF ratio was measured using an HTRF plate reader. The IC50 value of the compound was calculated, taking the inhibition rate without addition of the enzyme as 100% and the inhibition rate without addition of the test compound and with addition of an enzyme as 0%, by means of a logistic method. [0067] 2. PDKoc Enzyme Inhibitory Activity Human PI3Ka (12 ng/well, Millipore Corporation, Catalogue No. 14-602), phosphatidylinositol (0.2 ug/well), and the test compound were mixed in a 3 84-well plate in a reaction buffer (50 mM Hepes, 10 mM NaCl, 10 mM MgCl2, 2 mM EGTA, 2 mM DTT, pH 7.3) (total 10 ul), and incubated at 37°C for 3 hours. After the reaction, 10 uL of a Kinase-Glo Plus reagent (Promega, Catalogue No. V3772) was added thereto, and a luminescence was measured with a luminometer. The IC50 value of the compound was calculated, taking the inhibition rate without addition of the enzyme as 100% and the inhibition rate without addition of the test compound as 0%, by a logistic method. The results of the IC50 values (nM) of several representative compounds are shown in Table 1. In the Table, Ex represents Example Compound No. as described later of the test compounds. [0068] [Table 1] [0069] 3. Rat In vivo IL-2 Production Inhibition Test For the experiment, male LEW/CrlCrlj rats (Charles River Laboratories, Japan, Inc.) (6-week old, body weight 130 to 180 g) were used. The test compound was suspended in a 0.5% methyl cellulose solution and orally administered at 5 mL/kg; IL-2 production was induced by tail vein injection of Concanavalin A (Funakoshi Corporation, Catalogue No. L-1000) at a dose of 15 mg/kg. The test was carried out according to the protocol shown below. At 2 hours or 16 hours before administration of Concanavalin A, the test compound was orally administered to rats. At 3 hours after administration of Concanavalin A, blood was collected. The IL-2 concentration in blood was quantified using an ELISA kit (R&D Systems, Inc., Catalogue No. DY502E). An inhibition rate was calculated from the amount of IL-2 produced in a group administered with the test compound with respect to the amount of the IL-2 produced in a control group administered with a vehicle. [0070] As a result, it was confirmed that when the test compounds (10 mg/kg) were administered, for example, 2 hours before the administration of Concanavalin A, the several representative compounds of Examples 10, 29, 33, 34, 37, 43-1, and A4 exhibited inhibitory activities of 77%, 51%, 75%, 72%, 81%, 73%, and 58%, respectively, and had excellent IL-2 production inhibitory activities. [0071] 4. Rat B Cell Proliferation Inhibition Test Spleen cells (1 .Ox 105 cells/well) prepared from male LEW/CrlCrlj rats (Charles River Laboratories, Japan, Inc.), mouse F(ab')2 fragment anti-rat IgM (3 u.g/well, SouthernBiotech Associates, Inc., Catalogue No. 3082-14) and the test compound dissolved in DMSO (final DMSO concentration 0.1%) were mixed in a 96-well plate using a 10% FCS-containing RPMI-1640 culture medium (total 200 uL). They were cultured in a CO2 incubator for 48 hours and [3H]thymidine (925 GBq/mmol, Moravek Biochemicals, Inc., Catalogue No. MT6038) was added thereto at 0.037 MBq/well at 4 hours before completion of culture. Cells were harvested in a GF/C glass filter using a cell harvester, and a radioactivity on the filter was measured using a liquid scintillation counter. The IC50 value of the compound was calculated, taking the dpm (disintegration per minute) without addition of IgM as an inhibition rate of 100% and the dpm without addition of the test compound as an inhibition rate of 0%, by a logistic method. The results of several representative compounds are shown in Table 2. [0072] [Table 2] [0073] As shown in the tests above, it was confirmed that several representative compounds have excellent PI3K8 selective inhibitory action, and/or IL-2 production inhibitory action, and/or B cell proliferation inhibitory action (including an activation inhibitory action). Accordingly, the compound of the formula (I) can be used as an agent for preventing or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and/or hematologic tumor. [0074] Furthermore, since the compound of the formula (I) is a PI3K8 inhibitor having a significantly potent PI3K5 inhibitory action than a PDKa inhibitory action, it can be an excellent immunosuppressing agent which does not cause insulin resistance based on the PI3Ka inhibitory action. [0075] The various types of organs include the kidney, liver, and heart. The rejection reaction in organ transplantation involves chronic rejection and acute rejection, and its mechanism is largely classified into antibody-related rejection and T cell-related rejection. The compound of the formula (I) or a salt thereof is useful particularly as an agent for preventing and/or treating antibody-related rejection. [0076] A pharmaceutical composition containing one or two or more kinds of the compound of the formula (I) or a salt thereof as an active ingredient can be prepared using excipients that are usually used in the art, that is, excipients for pharmaceutical preparations, carriers for pharmaceutical preparations, and the like according to the methods usually used. Administration can be accomplished either by oral administration via tablets, pills, capsules, granules, powders, solutions, or the like, or parenteral administration, such as use of injections such as intraarticular, intravenous, and intramuscular injections, suppositories, eye drops, eye ointments, transdermal liquid preparations, ointments, transdermal patches, transmucosal liquid preparations, transmucosal patches, inhalers, and the like. [0077] The solid composition for use in the oral administration is used in the form of tablets, powders, granules, or the like. In such a solid composition, one or more active ingredient(s) are mixed with at least one inactive excipient such as lactose, mannitol, glucose, hydroxypropyl cellulose, microcrystalline cellulose, starch, polyvinylpyrrolidone, and/or magnesium aluminometasilicate. In an ordinary method, the composition may contain inactive additives, such as a lubricant such as magnesium stearate, a disintegrating agent such as sodium carboxymethyl starch, a stabilizer, or a solubilization assisting agent. If necessary, tablets or pills may be coated with sugar or a film of a gastric-soluble or enteric coating substance. The liquid composition for oral administration contains pharmaceutically acceptable emulsions, solutions, suspensions, syrups, elixirs, or the like, and also contains generally used inert diluents, for example, purified water and ethanol. In addition to the inert diluent, the liquid composition may also contain auxiliary agents such as a solubilization assisting agent, a moistening agent, and a suspending agent, sweeteners, flavors, aromatics, or antiseptics. [0078] The injections for parenteral administration include sterile aqueous or non-aqueous solutions, suspensions and emulsions. The aqueous solvent includes, for example, distilled water for injection and physiological saline. Examples of the non-aqueous solvent include propylene glycol, polyethylene glycol, plant oils such as olive oil, alcohols such as ethanol, Polysorbate 80 (Japanese Pharmacopeia), and the like. Such a composition may further contain a tonicity agent, an antiseptic, a moistening agent, an emulsifying agent, a dispersing agent, a stabilizer, or a solubilizing assisting agent. These are sterilized, for example, by filtration through a bacteria retaining filter, blending of a bactericide, or irradiation. In addition, these can also be used by preparing a sterile solid composition, and dissolving or suspending it in sterile water or a sterile solvent for injection prior to its use. [0079] The agent for external use includes ointments, plasters, creams, jellies, poultices, sprays, lotions, eye drops, and eye ointments. The agents contain generally used ointment bases, lotion bases, aqueous or non-aqueous liquid preparations, suspensions, and emulsions. Examples of the ointment bases or the lotion bases include polyethylene glycol, propylene glycol, white vaseline, bleached beeswax, polyoxyethylene hydrogenated castor oil, glyceryl monostearate, stearyl alcohol, cetyl alcohol, lauromacrogol, and sorbitan sesquioleate. [0080] As the transmucosal agents such as an inhaler and a transnasal agent, those in the form of a solid, liquid, or semi-solid state are used, and can be prepared in accordance with a conventionally known method. For example, a known excipient, and also a pH adjusting agent, an antiseptic, a surfactant, a lubricant, a stabilizer, a thickening agent, or the like may be appropriately added thereto. For their administration, an appropriate device for inhalation or blowing can be used. For example, a compound may be administered alone or as a powder of formulated mixture, or as a solution or suspension in combination with a pharmaceutically acceptable carrier, using a known device or sprayer, such as a measured administration inhalation device. A dry powder inhaler or the like may be for single or multiple administration use, and a dry powder or a powder-containing capsule may be used. Alternatively, this may be in a form such as a pressurized aerosol spray which uses an appropriate propellant, for example, a suitable gas such as chlorofluoroalkane, hydrofluoroalkane, and carbon dioxide. [0081] Typically, in oral administration, the daily dose is appropriately from about 0.001 to 100 mg/kg, preferably from 0.1 to 30 mg/kg, and more preferably 0.1 to 10 mg/kg, per body weight, administered in one portion or in 2 to 4 separate portions. In the case of intravenous administration, the daily dose is suitably administered from about 0.0001 to 10 mg/kg per body weight, once a day or two or more times a day. In addition, a transmucosal agent is administered at a dose from about 0.001 to 100 mg/kg per body weight, once a day or two or more times a day. The dose is appropriately decided in response to the individual case by taking the symptoms, the age, and the gender, and the like into consideration. [0082] Although varying depending on administration routes, dosage forms, administration sites, or the types of excipients and additives, the pharmaceutical composition of the present invention contains 0.01 to 100% by weight, and in a certain embodiment, 0.01 to 50% by weight of one or more kinds of the compound of the formula (I) or a salt thereof, which is an active ingredient. [0083] The compound of the formula (I) can be used in combination with various agents for treating or preventing the diseases, in which the compound of the formula (I) is considered effective. In such use in combination, drugs may be administered simultaneously or separately in succession or at desired time intervals. Formulations for simultaneous administration may be in either mixed or have separate forms. (Examples) [0084] Hereinbelow, the preparation methods for the compound of the formula (I) and the starting compounds thereof will be described in more detail with reference to Examples, but the present invention is not limited to the compounds described in the Examples below. Further, the production processes for the starting compounds will be each described in Preparation Examples. In addition, the preparation methods for the compound of the formula (I) are not limited to the preparation methods of the specific Examples shown below, but the compound of the formula (I) can be prepared by a combination of the preparation methods or a method that is apparent to a person skilled in the art. [0085] Furthermore, the following abbreviations may be used in some cases in Preparation Examples, Examples, and Tables below. PEx: Preparation Example No., Ex: Example No., Syn: Example No. prepared by the same method, PSyn: Preparation Example No. prepared by the same method, Str: Structural formula, DAT: Physicochemical data, ESI+: m/z values in mass spectroscopy (Ionization ESI, representing (M+H)+ unless otherwise specified), ESI-: m/z values (Ionization ESI, representing (M-H)' unless otherwise specified), NMR1: 8 (ppm) in 'H NMR in DMSO-d6, NMR2: 8 (ppm) in ]H NMR in CDC13, s: singlet (spectrum), d: doublet (spectrum), t: triplet (spectrum), q: quartet (spectrum), br: broad line (spectrum) (e.g.: br-s), RT: retention time (min) in HPLC, [M] in Preparation Examples and Examples: [mol/L], SFC preparative: preparative supercritical fluid chromatography, DEA: diethylamine. Furthermore, for example, a description of "26+44" in Syn of Example Tables indicates that preparation is performed by the same method as in Example 26, and subsequently the product is prepared by the same method as in Example 44 as a starting material. Further, in Preparation Example Tables, there is, for example, a description of Syn. 87 in the PSyn column of Preparation Example 148, indicating that Preparation Example 148 is prepared by the same method as in Example 87. In Example Tables, there is, for example, a description of PSyn. 8 in the Syn column of Example 295, indicating that Example 295 is prepared by the same method as in Preparation Example 8. HC1 in the structural formula denotes hydrochloride and the numeral before HC1 denotes a molar ratio. For example, 2HC1 means dihydrochloride. Further, Me in the structural formula denotes a methyl group, Et denotes an ethyl group, Ph denotes a phenyl group, iBu denotes an isobutyl group, tBu denotes a tert-butyl group, and Boc denotes a tert-butoxycarbonyl group. The compound having "*" in the structure indicates that the compound is an optically active substance. [0086] Preparation Example 1 To a solution of 4,6-dichloro-2-(methylsulfanyl)pyrimidine (5 g) inN,N-dimethylformamide (50 mL) were added potassium carbonate (5.3 g) and 2-(difluoromethyl)-lH-benzimidazole (3.9 g), and the mixture was stirred at room temperature for 5 hours. To the reaction mixture was added water, followed by extraction with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure and then the residue was purified by silica gel column chromatography (hexanerethyl acetate) to obtain 1 -[6-cUoro-2-(memylsiUfanyl)pyrimidin-4-yl]-2-(difluoromethyl)-1H-benzimidazole (5.49 g) as a white powder. [0087] Preparation Example 2 To a solution of l-[6-cMoro-2-(memylsulfanyl)pyrimidin-4-yl]-2-(difluoromethyl)-lH-benzimidazole (2.2 g) in N,N-dimethylformamide (11 mL) were added potassium carbonate (1.4 g) and morpholine (0.88 mL), and the mixture was stirred at room temperature for 1 hour. To the reaction solution was added water, followed by extraction with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure and then the residue was purified by silica gel column chromatography (hexane:ethyl acetate) to obtain 2-(difluoromethyl)-l-[2-(methylsulfanyl)-6-morpholin-4-ylpyrimidin-4-yl]-lH-benzimidazole (2.1 g) as a white powder. [0088] Preparation Example 3 To a solution of 2-(difluoromethyl)-l-[2-(methylsulfanyl)-6-morpholin-4-ylpyrimidin-4-yl]-lH-benzimidazole (3 g) in dichloromethane (60 mL) was added m-chloroperbenzoic acid (75% wet) (1.9 g) under ice-cooling, and the mixture was stirred at 0°C for 15 minutes. To the reaction mixture was added a saturated aqueous sodium bicarbonate solution, followed by extraction with dichloromethane. The organic layer was washed with water and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure and then the residue was purified by silica gel column chromatography (chloroform:methanol) to obtain 2-(difluoromethyl)-l-[2-(memylsulfinyl)-6-morpholm-4-ylpyrimidin-4-yl]-lH-benzimidazole (2.8 g) as a pale yellow amorphous substance. [0089] Preparation Example 4 To a solution of 2-(difluoromethyl)-l-[2-(methylsulfanyl)-6-morpholin-4-ylpyrimidin-4-yl]-lH-benzimidazole (2.1 g) in dichloromethane (21 mL) was added m-chloroperbenzoic acid (75% wet) (2.7 g) under ice-cooling and the mixture was stirred at 0°C for 15 minutes. To the reaction mixture was added a saturated aqueous sodium bicarbonate solution, followed by extraction with dichloromethane. The organic layer was washed with water and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure and then the residue was purified by silica gel column chromatography (chloroformrmethanol) to obtain 2-(difluoromethyl)-l-[2-(memylsulfonyl)-6-morpholm-4-ylpyrimidin-4-yl]-lH-benzirnidazole (2.27 g) as a pale yellow amorphous substance. [0090] Preparation Example 5 To a mixture of l-[6-chloro-2-(methylsulfanyl)pyrimidin-4-yl]-2-(difluoromethyl)-lH-benzimidazole (1 g) and N,N-dimethylacetamide (10 mL) were added tert-butyl 4-(hydroxymethyl)piperidine-l-carbamate (1 g) and cesium carbonate (3 g), and the mixture was stirred at 120°C for 3 hours. The reaction mixture was poured into water, followed by extraction with hexane-ethyl acetate (1:1). The organic layer was washed with water and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure and then the residue was purified by silica gel column chromatography (hexane:ethyl acetate) to obtain tert-butyl 4-[({6-[2-(difluorornethyl)-lH-benzimidazol-1 -yl]-2-(methylsulfanyl)pyrimidin-4-yl} oxy)methyl]piperidine-1 -carbamate (680 mg) as a white amorphous substance. [0091] Preparation Example 6 N-(2-{[6-Chloro-2-(methylsulfanyl)pyrimidin-4-yl]amino}-5-methylphenyl)acetamide (270 mg) was dissolved in a mixed solvent of ethanol (2.8 mL) and 1,4-dioxane (2.8 mL), and 6 M hydrochloric acid (9.6 mL) was added thereto, followed by heating and refluxing for 3 hours. After air-cooling to room temperature, the pH was adjusted to 6 to 7 using saturated aqueous sodium bicarbonate, followed by extraction with ethyl acetate. The organic layer was dried over anhydrous magnesium sulfate and the solvent was evaporated under reduced pressure to obtain N1-[6-chloro-2-(methylsulfanyl)pyrimidin-4-yl]-4-methylbenzene-l,2-diamine (230 mg). [0092] Preparation Example 7 A mixture of 2-(methylsulfanyl)-6-(morpholin-4-yl)pyrimidin-4-amine (500 mg), 2-bromo-l-methyl-3-nitrobenzene (1 g), tris(dibenzylideneacetone)dipalladium (0) (202 mg), (9,9-dimethyl-9H-xanthen-4,5-diyl)bis(diphenylphosphine) (192 mg), and cesium carbonate (1.0 g) in toluene was stirred in a microwave reactor at 140°C for 1 hour. The reaction mixture was filtered through celite and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (hexane:ethyl acetate) to obtain N-(2-methyl-6-nitrophenyl)-2-(me%lsulfanyl)-6-(morpholin-4-yl)pyrimidin-4-amine (756 mg) as a yellow powder. [0093] Preparation Example 8 N<2-Me1hyl-6-nitrophenyl)-2, -C(0)-NR5-ALK-0-ALK-, -NR5-C(0)-ALK-, -NR5-C(0)-ALK-C(O)-, -NR5-C(0)-ALK-0-ALK-, -ALK-C(0)-NR5-, -ALK-NR5-C(0)-, -C(0)-0-, -ALK-C(0)-0-, -C(0)-0-ALK-5 -C(0)-ALK-, -ALK-C(O)-, -NR5-C(0)-ALK-NR5-, or -C(0)-, R8's are the same as or different from each other and are H; cycloalkyl, phenyl, pyridyl, or a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen; -R9 or -ALK-L4-R9, in which R9 is lower alkyl which may be substituted with one or more substituents selected from the group consisting of -0-R6, -S-R6, -CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, -cycloalkyl, phenyl, and a non-aromatic heterocycle, and L4 is -C(0>, -C(0)-NR5-, -NR5-, -NR5-S(0)2-, -NR5-C(0)-, -NR5-C(0)-0-, -0-, -S-, or -S(0)m-, provided that in a case where R1 has the following formula (II), all of B's are CH, W is NH or 0, B1 is a bond or lower alkylene, and B2 is a bond or lower alkylene, [Chem. 11] R10 is -C(0)-(lower alkylene substituted with -NH-C(0)-0-lower alkyl)-S-lower alkyl, -C(0)-non-aromatic heterocycle, -C(0)-lower alkylene-NH-lower alkylene-(cycloalkyl which may be substituted with -OH), -C(0)-lower alkylene-NH-(cycloalkyl which may be substituted with a group selected from the group consisting of lower alkyl and -OH), -C(0)-lower alkylene-NH-non-aromatic heterocycle, -C(0)-lower alkylene-NH-(lower alkyl substituted with -OH), or -C(0)-(cycloalkyl substituted with one or more substituents selected from the group consisting of -NH2, -N(lower alkyl)2, and -NH-C(0)-0-lower alkyl), or R4 and R10 form a 4- to 8-membered monocyclic heterocyclic group containing 1 to 4 hetero atoms selected from O, S, and N, together with N to which they are bonded, and are further substituted with at least one substituent selected from a Group D2, in which the Group D2 consists of: (a) -0-(lower alkyl substituted with one or more substituents selected from the group consisting of-O-R6, -S-R6, -CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, cycloalkyl, and a non-aromatic heterocycle), -0-(cycloalkyl, phenyl, pyridyl, or a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen), and -0-ALK-L4-R9, (b) -SR8, (c) -N02, (d) -NRnR7, in which R7 is -R8, -C(0)-R8, -C(0)-C(0)-N(R8)2, -C(0)-0-R8, and -S(0)2-R8, and R11 is lower alkyl substituted with one or more substituents selected from the group consisting of -OH, -O-lower alkyl, -CN, halogen, cycloalkyl, and phenyl, (e) -C(0)-R8, (i) -S(0)2-R8 and -S(0)2-N(R8)2, (g) -C(0)-0-(lower alkyl substituted with one or more substituents selected from the group consisting of-O-R6, -S-R6, -CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, cycloalkyl, phenyl, pyridyl, and a non-aromatic heterocycle), -C(0)-0-(cycloalkyl, phenyl, or a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen), and -C(0)0-ALK-L4-R9, (h) -C(0)-N(R8)2, (i) -C(0)-C(0)-N(R8)2, (j) -0-C(0)-(lower alkyl substituted with one or more substituents selected from the group consisting of-O-R6, -S-R6, -CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(0)-0-R6, cycloalkyl, phenyl, pyridyl, and a non-aromatic heterocycle), -O-C(O)-(cycloalkyl, phenyl, or a non-aromatic heterocycle, each of which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen), -0-C(0)-ALK-L4-R9, -0-C(0)-NH-C(=NH)-NH2, and -O-C(O)-N(R8)2, (k) lower alkyl substituted with one or more substituents selected from the group consisting of-CN, -N(R6)2, -C(0)-R6, -C(0)-0-R6, -C(0)-N(R6)2, -N(R6)-C(O)-0-R6, -S(0)2-lower alkyl, cycloalkyl, and phenyl, (1) cycloalkyl which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen, (m) aryl which may be substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen, (n) an aromatic heterocycle substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen, and (o) a non-aromatic heterocycle substituted with one or more substituents selected from the group consisting of lower alkyl, -OH, -O-lower alkyl, -CN, and halogen.) [Claim 2] The compound or a salt thereof according to claim 1, wherein R1 is -NH-lower alkylene-C(0)-OH or -L'-L2-Y, L1 is -lower alkynylene-, -NR5-, -NR5-S(0)2-, -NR5-C(O)-, -0-, -S-, or -S(0)m-, m is 1 or 2, L2 is a bond, -ALK-X2-, -ALK-NR6-C(0)-, -ALK-NR6-C(0)-0-ALK-, -ALK-S(0)m-X1-, or -ALK-C(0)-X2-, ALK's are the same as or different from each other and are lower alkylene which may be substituted with one or more substituents selected from the group consisting of -OH, -O-lower alkyl, -CN, halogen, and cycloalkyl, X1 is a bond, -NR6-, or -NR6-ALK-, X2's are the same as or different from each other and are a bond, -NR6-, -NR6-ALK-, -0-, -S-, -NR6-ALK-0-, -NR6-ALK-C(0)-NR6-, or -NR6-ALK-C(0)-, R4's are the same as or different from each other and are H, or lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -CN, halogen, and cycloalkyl, R5's are the same as or different from each other and are -R4, lower alkenyl, or cycloalkyl, R6's are the same as or different from each other and are H, cycloalkyl, a non-aromatic heterocycle which may be substituted with lower alkyl, or lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, -0-lower alkyl, -CN, halogen, -N(R4)2, cycloalkyl, and a non-aromatic heterocycle, Y is lower alkyl which may be substituted with one or more substituents selected from the group consisting of-OH, -O-lower alkyl, -N(lower alkyl)2, and -C(0)-N(lower alkyl)2, cycloalkyl which may be substituted with one or more substituents selected from the Group Dl, or a non-aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl, provided that L2 is -ALK-X2a-, -ALK-NR6-C(0)-, -ALK-NR6-C(0)-0-ALK-, -ALK-S(0)m-X1-, or -ALK-C(0)-X2-, in which in a case where X2a is -NR6-, -NR6-ALK-, -0-, -S-, -NR6-ALK-0-, -NR6-ALK-C(0)-NR6-, or -NR6-ALK-C(0)-, further Y is aryl which may be substituted with one or more substituents selected from the Group Dl or an aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl. [Claim 3] The compound or a salt thereof according to claim 2, wherein R1 is -L1-L2-Y, L1 is -NR5-, -NR5-S(0)2-, -NR5-C(0)-, or -0-, in which R5 is H or lower alkyl, L2 is a bond, -ALK-, -ALK-S-, -ALK-S(0)m-X1-, or -ALK-C(0)-X2-, in which X1 is a bond or-NR6-, X2 is a bond, -NR6-, -NR6-ALK-, or -0-, ALK is lower alkylene, R6 is H or lower alkyl, and Y is cycloalkyl which may be substituted with one or more substituents selected from the Group Dl, or a non-aromatic heterocycle which may be substituted with one or more substituents selected from the Group Dl. [Claim 4] The compound or a salt thereof according to claim 3, wherein -L'-L2- is-NH- or -0-. [Claim 5] The compound or a salt thereof according to claim 4, wherein all of B 's are CH and n is 0. [Claim 6] The compound or a salt thereof according to claim 5, wherein A1 and A3 are N and A2 is CH. [Claim 7] The compound or a salt thereof according to claim 5, wherein A2 and A3 are N and A1 is CH. [Claim 8] The compound or a salt thereof according to claim 1, wherein the compound is methyl {(3S)-1 -[trans-4-({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} oxy)cyclohexyl] -2-oxopyrrolidin-3 -yl} carbamate,methyl {(3R)-1 -[trans-4-( {6- [2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} oxy)cyclohexyl] -2-oxopyrrolidin-3 -yl} carbamate, ethyl {(3R)-1 -[trans-4-({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4 yl}oxy)cyclohexyl]-2-oxopyrrolidin-3-yl}carbamate, [(3 S)-3 -({6- [2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidm-4-yl}aniino)pyrrolidin-l-yl][(2R)-tefrahydrofuran-2-yl]methanone, [(3S)-3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl}amino)pyrrolidin-l-yl](tetrahydro-2H-pyran-4-yl)methanone, methyl {(3 S)-1 -[trans-4-( {4-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-6-(morpholin-4-yl)pyrimidin-2-yl} amino)cyclohexyl] -2-oxopyrrolidin-3 -yl} carbamate, methyl {(3 R)-l-[trans-4-({ 4-[2-(difluoromethyl)-l H-benzimidazol-1-yl]-6-(morpholin-4-yl)pyrimidin-2-yl}amino)cyclohexyl]-2-oxopyrrolidin-3-yl}carbamate, methyl {(3R)-l-[trans-4-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl}amino)cyclohexyl]-2-oxopyrrolidin-3-yl}carbamate,l-[(3S)-3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl) pyrimidin-4-yl} amino)pyrrolidin-1 -yl]-2-(tetrahydrofuran-2-yl)ethanone,l-[(3S)-3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] -2-(tetrahydro-2H-pyran-4-y l)ethanone,1 - [3-( {6- [2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} oxy)azetidin-1 -yl]-2-(tetrahydrofuran-2-yi)ethanone,methyl 4-{[(3 S)-3-({ 6-[2-(difluoromethyl)-l H-benzimidazol-1-yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] carbonyl} piperidine-1 -carboxylate,[(3S)-3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl} oxy)pyrrolidin-1 -yl] (tetrahydrofuran-3 -yl)methanone,4- {[(3 S)-3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} oxy)pyrrolidin-1 -yl] carbonyl} -1 -methylpyrrolidin-2-one,-( 1 -acetylpiperidin-4-yl)- l-[(3S)-3-({6- [2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-y 1} amino)pyrrolidin-1 -yl] ethanone,[(3S)-3-({6- [2-(difluoromethyl)-1 H-benzimidazol-1 -y 1] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] (tetrahydrofuran-3 -y l)methanone,4- {[(3 S)-3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] carbonyl} -1 -methylpyrrolidin-2-one,1 -[(3S)-3-({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] -2-(piperidin-1 -yl)ethanone,(5S)-5-{[3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl} oxy)azetidin-1 -yl] carbonyl} pyrrolidin-2-one,(5S)-5-{[3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)azetidin-1 -yl]carbonyl} pyrrolidin-2-one,2-( 1 -acetylpiperidin-4-yl)-1-[3-({6- [2-(difluoromethy 1)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)azetidin-1 -yl] ethanone,[3 -({6-[2-(difluoromethyl)-1 H-benzimidazol-1 -yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)azetidin-1 -yl] (tetrahydrofiiran-3 -yl)methanone,4-{[3-({6- [2-(difluoromethy 1)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)azetidin-1 -yl]carbonyl} -1 -methylpyrrolidin-2-one,[(3S)-3-({6-[2-(difluoromethyl)-lH-benzimidazol-l-yl]-2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-l -yl] [cis-4-(hydroxymethyl)cyclohexyl]methanone, or[(3 S)-3 -({6- [2-(difluoromethyl)-1 H-benzimidazol-1 -yl] -2-(morpholin-4-yl)pyrimidin-4-yl} amino)pyrrolidin-1 -yl] [trans-4-(hydroxymethyl)cyclohexyl]methanone. [Claim 9] A pharmaceutical composition comprising the compound or a salt thereof according to claim 1 and a pharmaceutically acceptable excipient. [Claim 10] A pharmaceutical composition for preventing or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, or hematologic tumor, comprising the compound or a salt thereof according to claim 1 and a pharmaceutically acceptable excipient. [Claim 11] Use of the compound or a salt thereof according to claim 1 for the manufacture of a pharmaceutical composition for preventing or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, or hematologic tumor. [Claim 12] Use of the compound or a salt thereof according to claim 1 for preventing and/or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, and hematologic tumor. [Claim 13] The compound or a salt thereof according to claim 1 for preventing or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, or hematologic tumor. [Claim 14] A method for preventing or treating rejection reactions in various organ transplantations, allergy diseases, autoimmune diseases, or hematologic tumor, comprising administering to a subject an effective amount of the compound or a salt thereof according to claim 1.