class vehicle {
  int wheels;
public:
  vehicle(int w = 4) : wheels(w) {}
  int max_speed() { return 60; }
};

class bicycle : public vehicle {
  int panniers;
public:
  bicycle(bool p = true) : vehicle(2), panniers(p) {}
  int max_speed() { return panniers ? 12 : 15; }
};