using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        bool? t = true;

        bool? f = false;

        bool? n = null;

        if(t == true)

        {

            Console.WriteLine("t is true");

        }

        if(f == false)

        {

            Console.WriteLine("f is false");

        }

        if(n != false)

        {

            Console.WriteLine("n is not false");

        }

        if(n != true)

        {

            Console.WriteLine("n is not true");

        }

    }

}