/in/foo.cc: In function 'int max_sum()':
/in/foo.cc:5:2: error: 'cin' was not declared in this scope
  cin >> N;
  ^~~
/in/foo.cc:6:2: error: 'vector' was not declared in this scope
  vector<int> v(N);
  ^~~~~~
/in/foo.cc:6:9: error: expected primary-expression before 'int'
  vector<int> v(N);
         ^~~
/in/foo.cc:10:10: error: 'v' was not declared in this scope
   cin >> v[i];
          ^
/in/foo.cc:13:12: error: 'v' was not declared in this scope
  int max = v[0];
            ^