cout << "\n size:" << left.size() << " " << right.size() << endl;
  while (left.size()>0 && right.size()>0) {
    cout << " left.front():" << left.front() << " right.front():" << right.front() << endl;
    if (left.begin() <= right.begin()) {
        res.push_back(left.front());
        left.erase(left.begin());
        cout << " push_left size:" << left.size() << endl;
    }
    else {
      res.push_back(right.front());
      right.erase(right.begin());
      cout << " push_right size:" << right.size() << endl;
    }
  }
  if (left.size() > 0) {
    res.insert(res.end(), left.begin(), left.end());
    cout << " push_left_back " << endl;
  }
  if (right.size() > 0) {
    res.insert(res.end(), right.begin(), right.end());
    cout << " push_right_back " << endl;
  }