View Compilation Error

0_0_17879522_23624.cpp:3:1: error: '_int64' does not name a type
 _int64 fun(int x)
 ^
0_0_17879522_23624.cpp: In function 'int main()':
0_0_17879522_23624.cpp:12:5: error: '_int64' was not declared in this scope
     _int64 sum=0,n,a,b,c;
     ^
0_0_17879522_23624.cpp:13:20: error: 'n' was not declared in this scope
  while(scanf("%d",&n)!=EOF)
                    ^
0_0_17879522_23624.cpp:15:2: error: 'a' was not declared in this scope
  a=fun(2*n);
  ^
0_0_17879522_23624.cpp:15:11: error: 'fun' was not declared in this scope
  a=fun(2*n);
           ^
0_0_17879522_23624.cpp:16:5: error: 'b' was not declared in this scope
     b=fun(n+1);
     ^
0_0_17879522_23624.cpp:17:2: error: 'c' was not declared in this scope
  c=fun(n);
  ^
0_0_17879522_23624.cpp:18:2: error: 'sum' was not declared in this scope
  sum=a/(b*c);
  ^