using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

         IEnumerable<string> words = new List<string>()

         {

             "apple",

             "Apple",

             "orange",

             "orange"

         };

        Console.WriteLine(string.Join(",", words.Distinct()));

    }

}