View Compilation Error

0_0_17880474_6527.cpp:3:1: error: '_int64' does not name a type
 _int64 fun(int x)
 ^
0_0_17880474_6527.cpp: In function 'int main()':
0_0_17880474_6527.cpp:12:5: error: '_int64' was not declared in this scope
     _int64 sum=0,a,b,c;
     ^
0_0_17880474_6527.cpp:20:2: error: 'a' was not declared in this scope
  a=fun(2*n);
  ^
0_0_17880474_6527.cpp:20:11: error: 'fun' was not declared in this scope
  a=fun(2*n);
           ^
0_0_17880474_6527.cpp:21:5: error: 'b' was not declared in this scope
     b=fun(n+1);
     ^
0_0_17880474_6527.cpp:22:2: error: 'c' was not declared in this scope
  c=fun(n);
  ^
0_0_17880474_6527.cpp:23:2: error: 'sum' was not declared in this scope
  sum=a/(b*c);
  ^