/in/foo.cc: In function 'int main()':
/in/foo.cc:6:1: error: 'cin' was not declared in this scope
 cin >> m >> n;
 ^~~
/in/foo.cc:11:1: error: 'cout' was not declared in this scope
 cout << m*n/k<<endl;
 ^~~~
/in/foo.cc:11:16: error: 'endl' was not declared in this scope
 cout << m*n/k<<endl;
                ^~~~