Longest word combination

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace SubstringSO
{
    class Program
    {
        static void Main(string[] args)
        {
            String input = "star, artifact, book, ctenophore, list, reply";
            String pattern = "[a-zA-Z]+";

            var words = Regex.Matches(input, pattern).Cast<Match>().Select(m => m.Value).Where(r => r.Length >= 2);

            Dictionary<string, string> lookup = new Dictionary<string, string>();

            string maxString = "";

            foreach (var word in words)
            {
                string initial = word.Substring(0, 2);
                string end = word.Substring(word.Length - 2, 2);
                if (!lookup.ContainsKey(initial))
                {
                    if (!lookup.ContainsKey(end))
                    {
                        lookup.Add(end, word);
                    }
                    else if (lookup[end].Length < word.Length)
                    {
                        lookup[end] = word;
                    }

                    if (word.Length > maxString.Length)
                        maxString = word;
                }
                else
                {
                    string newString = lookup[initial] + ", " + word;
                    if (!lookup.ContainsKey(end))
                    {
                        lookup.Add(end, newString);
                    }
                    else if (lookup[end].Length < newString.Length)
                    {
                        lookup[end] = newString;
                    }

                    if (newString.Length > maxString.Length)
                        maxString = newString;
                }
            }


            Console.WriteLine(maxString);
            Console.ReadKey();
        }
    }
}