using System;

using System.Net;

public class Program

{

    public static void Main()

    {

        string goodIp = "127.0.0.1";

        string badIp = "127.0.O.1";

        IPAddress ip;

        if (IPAddress.TryParse(goodIp, out ip))

        {

            Console.WriteLine("Start your server");

        }

        if (!IPAddress.TryParse(badIp, out ip))

        { 

            Console.WriteLine("Bad IP");

        }

    }

}