foo.cc: In function 'int main()':
foo.cc:4:2: error: 'cin' was not declared in this scope
  cin >> m >> n;
  ^~~
foo.cc:4:2: note: suggested alternative: 'main'
  cin >> m >> n;
  ^~~
  main
foo.cc:22:2: error: 'cout' was not declared in this scope
  cout << tol << endl;
  ^~~~
foo.cc:22:17: error: 'endl' was not declared in this scope
  cout << tol << endl;
                 ^~~~
foo.cc:22:17: note: suggested alternative: 'enum'
  cout << tol << endl;
                 ^~~~
                 enum

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。