#include <iostream>
using namespace std;

class Animal {                 // top level
  public:
    void breathe() { cout << "Breathing...\n"; }
};

class Mammal : public Animal { // middle level
  public:
    void feedMilk() { cout << "Feeding milk...\n"; }
};

class Dog : public Mammal {    // bottom level
  public:
    void bark() { cout << "Woof!\n"; }
};

int main() {
  Dog d;
  d.breathe();   // from Animal
  d.feedMilk();  // from Mammal
  d.bark();      // from Dog
  return 0;
}