using System;

public class Program

{

    public delegate void Action();

    public Action eventA;

    private int cnt = 0;

    public void Main()

    {

        cnt = 0;

        eventA -= Hello;

        eventA += Hello;

        eventA += Hello;

        eventA += Hello;

        eventA -= Hello;

        if(eventA!=null)

            eventA();

    }

    private void Hello()

    {

        Console.WriteLine("Hello World "+ (++cnt));

    }

}