View Compilation Error

0_0_37711429_17832.cpp: In function 'int main()':
0_0_37711429_17832.cpp:44:5: error: incomplete type 'std::ios {aka std::basic_ios<char>}' used in nested name specifier
     ios::sync_with_stdio(false);
     ^
0_0_37711429_17832.cpp:45:5: error: 'cin' was not declared in this scope
     cin.tie(0);
     ^
0_0_37711429_17832.cpp:46:5: error: 'cout' was not declared in this scope
     cout.tie(0);
     ^
0_0_37711429_17832.cpp:63:24: error: 'endl' was not declared in this scope
         cout << ans << endl;
                        ^