View Compilation Error

0_0_39397754_16796.cpp:5:1: error: '_int64' does not name a type
    5 | _int64 f_array(int);
      | ^~~~~~
0_0_39397754_16796.cpp: In function 'int main()':
0_0_39397754_16796.cpp:21:23: error: 'f_array' was not declared in this scope
   21 |                 res = f_array(n);
      |                       ^~~~~~~