using System;

​

public abstract  class A

{

    public abstract void Show();

}

public class B :A

{

    public override  void Show()

    {

        Console.WriteLine("Class B");

    }

}

​

public class C:B

{

    public override  void Show()

    {

        Console.WriteLine("Class C");

    }

}

public class Program

{

    public static void Main()

    {

        C ex = new C();

        A a = new C();

        a.Show();

        ex.Show();

        Console.WriteLine("Hello World");

    }

}