using System;
public class Program
{
    public static void Main(string[] args)
    {
        var dog = new Dog();
        var cat = new Cat();
        dog.eat();
        cat.eat();
        
        var owner = new Owner();
        owner.feed(dog);
        owner.feed(cat);
    }
}

public interface IAnimal
{
    void eat();
}

public class Dog : IAnimal
{
    public void eat()
    {
        Console.WriteLine("Dog eats.");
    }
}

public class Cat : IAnimal
{
    public void eat()
    {
        Console.WriteLine("Cat eats.");
    }
}

public class Owner
{
    public void feed(IAnimal animal)
    {
        animal.eat();
    }
}