View Compilation Error

0_0_26346996_5137.cpp: In function 'int main()':
0_0_26346996_5137.cpp:7:5: error: '_int64' was not declared in this scope
     _int64 n;
     ^
0_0_26346996_5137.cpp:8:23: error: 'n' was not declared in this scope
  while(scanf("%I64d",&n)){
                       ^
0_0_26346996_5137.cpp:9:10: error: expected ';' before 'sum'
   _int64 sum=n*(n+1)/2;
          ^
0_0_26346996_5137.cpp:10:20: error: 'sum' was not declared in this scope
   printf("%I64d\n",sum);
                    ^