using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        List<string> ds = new List<string>() {

            "ds1",

            null,

            "momsds",

            "ds1",

            null

        };

        ds.Distinct().ToList().ForEach(ds => Console.WriteLine(ds));

    }

}