using System;

using System.Text.RegularExpressions;

public class Program

{

        private static Regex _ApiServiceDisplayNameRegex = new Regex(@"^(Start\.)?(?<capturedGroup>.+?)(\.|\.\2)?(End)?$", RegexOptions.IgnoreCase | RegexOptions.Multiline);

    public static void Main()

    {

        Console.WriteLine(_ApiServiceDisplayNameRegex.Match("Start.Word.WordEnd").Groups["capturedGroup"].Value);

    } 

}