using System;

using System.Linq; // add this for Distinct() use

public class Program

{

    public static void Main()

    {

        var siteStringInput = "Site 2100, Site 2100, Site 2100, Site 2100, Site 9999";

        // split string into array and trim leading whitespace

        var sites = siteStringInput.Split(',').Select(x => x.Trim()).ToList();

        // get distinct sites

        var distinctSites = sites.Distinct().ToList();

        foreach (var s in distinctSites)

        {

            Console.WriteLine(s);

        }

    }

}