using System;

class TestClass

{

    delegate void CustomDel(string s);

    public static void Hello(string s)

    {

        Console.WriteLine("Hello "+s);

    }

    public static  void Goodbye(string s)

    {

        Console.WriteLine("GoodBye "+s);

    }

    public static void Main()

    {

        CustomDel a,b,c,d;

        a=Hello;

        b=Goodbye;

        c=a+b;

        d=c-a;

        a("a");b("b");c("c");d("d");

    }

}