class Correct
    {
        static void Main(string[] args)
        {
            Animal animal = new Chicken();
            Console.WriteLine(animal.GetCountOfLeg());
            animal = new Dog();
            Console.WriteLine(animal.GetCountOfLeg());
        }
    }
    public abstract class Animal
    {
        public abstract string GetCountOfLeg();
    }
    public class Dog : Animal
    {
        public override string GetCountOfLeg()
        {
            return "4";
        }
    }
    public class Chicken : Dog
    {
        public override string GetCountOfLeg()
        {
            return "2";
        }
    }