using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

}

​

public sealed class Singleton

{

    private static Singleton obj;

    private Singleton()

    {

    }

    public static Singleton CreateInstance()

    {

        if(obj==null)

            obj=new Singleton();

        return obj;     

    }

}