View Compilation Error

0_0_39265512_19566.cpp:6:1: error: '__int64_t' does not name a type; did you mean 'uint64_t'?
    6 | __int64_t f(int num) {
      | ^~~~~~~~~
      | uint64_t
0_0_39265512_19566.cpp: In function 'int main()':
0_0_39265512_19566.cpp:16:17: error: 'f' was not declared in this scope
   16 |         cout << f(n) << endl;
      |                 ^