using System;

using System.Net;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var ipDict = new HashSet<IPAddress>();

        ipDict.Add(IPAddress.Parse("001.001.001.001"));

        if (ipDict.Contains(IPAddress.Parse("1.1.1.1")))

        {

            Console.WriteLine("IP address found in HashSet");

        }

    }

}