View Compilation Error

0_0_34172733_1293.cpp: In function 'int main()':
0_0_34172733_1293.cpp:64:94: error: 'inv' was not declared in this scope
         printf("%llu\n",(ull(Check(n + 1) - Check(2)) + (n + 4) % MOD * (n - 1) % MOD * inv(2) % MOD) % MOD);
                                                                                              ^