Unable to understand multicast delegates

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Delgates_Ex1
{

    public delegate void ExampleDelgate(int x, int y);


    class Democlass
    {
        public void Add(int x, int y)
        {

            Console.WriteLine(x+y);
            

        }


        public static void mul(int x, int y)
        {
            Console.WriteLine(x*y);

        }

    }


    class Program
    {
        public static void Sub(int x, int y)
        {

            Console.WriteLine(x -y);


        }



        static void Main(string[] args)
        {
            Democlass d = new Democlass();

            ExampleDelgate e1 = new ExampleDelgate(d.Add);  // I know here I am doing  instantiation of the delegate

            ExampleDelgate e2 = new ExampleDelgate(Democlass.mul);

            ExampleDelgate e3 = e1 + e2;


            e3 = e1 + e2 + e3;  // When I execute the line i get twice i.e out put would be  30 200 30 200 can any one explain me what is happening here. Basically I am trying to
            //understand Mutlicast delegates and when i remove +e3 i just get only once


            e3(20, 10);  // and here I am doing Delegate Invocation

        }
    }
}