using System;

public class Program

{

    public static void Main()

    {

        ClassA a = new ClassA();

        a.PrintMessage();

        a.PrintMessageAbstract();

    }

    abstract class MyAbstractClass

    {

        private string message = "Hello C#";

        public void PrintMessage()

        {

            Console.WriteLine(message);

        }

        public abstract void PrintMessageAbstract();

    }

    class ClassA : MyAbstractClass

    {

        public override void PrintMessageAbstract()

        {

            Console.WriteLine("C# is fun!");

        }

    }

}