using System;           

public class Program

{

    public class Singleton

    {

        private static int counter = 0;

        private static Singleton instance = null;

        public static Singleton GetInstance

        {

            get

            {

                if (instance == null)

                    instance = new Singleton();

                return instance;

            }

        }     

        private Singleton()

        {

            counter++;

            Console.WriteLine("Counter Value " + counter.ToString());

        }

        public void PrintDetails(string message)

        {

            Console.WriteLine(message);

        }

        public class DerivedSingleton : Singleton

        {

        }

    }

    public static void Main()

    {

            Singleton fromTeachaer = Singleton.GetInstance;

            fromTeachaer.PrintDetails("From Teacher");

            Singleton fromStudent = Singleton.GetInstance;

            fromStudent.PrintDetails("From Student");

        Singleton.DerivedSingleton derivedObj=new Singleton.DerivedSingleton();

        derivedObj.PrintDetails("From Derived class");

            Console.ReadLine();

    }

}