View Compilation Error

0_0_34066423_12910.cpp:4:1: error: '_int64' does not name a type
 _int64 C(_int64 a, _int64 b) {
 ^
0_0_34066423_12910.cpp: In function 'int main()':
0_0_34066423_12910.cpp:19:3: error: '_int64' was not declared in this scope
   _int64 res = 0;
   ^
0_0_34066423_12910.cpp:22:4: error: 'res' was not declared in this scope
    res += (_int64)(i - 1) * C(n, i);
    ^
0_0_34066423_12910.cpp:22:35: error: 'C' was not declared in this scope
    res += (_int64)(i - 1) * C(n, i);
                                   ^
0_0_34066423_12910.cpp:25:11: error: 'res' was not declared in this scope
   cout << res << endl;
           ^