using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main(string[] args)

    {

        XXX(null);

    }

    public static void XXX(IEnumerable<string> args)

    {

        if (args?.Count() == 0)

            {

                Console.WriteLine("Hello, world!");

            }

            Console.WriteLine("goodbye, world!");

    }

}