foo.cc: In function 'int main()':
foo.cc:25:2: error: 'ios' has not been declared
  ios::sync_with_stdio(false);
  ^~~
foo.cc:33:2: error: 'cin' was not declared in this scope
  cin>>n>>m;
  ^~~
foo.cc:33:2: note: suggested alternative: 'main'
  cin>>n>>m;
  ^~~
  main
foo.cc:52:2: error: 'cout' was not declared in this scope
  cout<<sum<<endl<<time;
  ^~~~
foo.cc:52:13: error: 'endl' was not declared in this scope
  cout<<sum<<endl<<time;
             ^~~~
foo.cc:52:13: note: suggested alternative: 'enum'
  cout<<sum<<endl<<time;
             ^~~~
             enum