using System;

​

public class Program

{

    public static void Main()

    {

        var publisher = new Publisher();

        new Subscriber(publisher);

        new Subscriber1(publisher);

        new Subscriber(publisher);

        new Subscriber1(publisher);

        new Subscriber(publisher);

        new Subscriber1(publisher);

        publisher.DoPublish();

    }

}

​

public class Publisher

{

    public Action MethodToBePublished;

    public void DoPublish()

    {

        MethodToBePublished();

    }

}

public class Subscriber {

    public Subscriber(Publisher publisher){

        publisher.MethodToBePublished += SayHello;

    }

    private void SayHello(){

        Console.WriteLine("Hello from SUBSCRIBER1 OK");

    }

}

public class Subscriber1 {

    public Subscriber1(Publisher publisher){

        publisher.MethodToBePublished += SayHello;

    }

    private void SayHello(){

        Console.WriteLine("Hello from SUBSCRIBER2 OK OK");

    }

}