DouKaku?

class Word
{
    public string Tango{get;set;}
    public bool Used{get;set;}

    public Word(string t)
    {
        Tango = t;
        Used = false;
    }

    public char First()
    {
        return Tango.First();
    }

    public char Last()
    {
        return Tango.Last();
    }
}

class Program
{
    static Dictionary<char, List<Word>> wordDic = new Dictionary<char, List<Word>>();
    static List<Word> wordList = new List<Word>();
    static int count = 0;
    static int maxcount = 0;

    static void Add(Word word)
    {
        List<Word> list;

        if (wordDic.ContainsKey(word.First()))
        {
            list = wordDic[word.First()];
        }
        else
        {
            list = new List<Word>();
            wordDic[word.First()] = list;
        }

        list.Add(word);
    }

    static void Main(string[] args)
    {
        using (StreamReader sr = new StreamReader("D:\\tango.txt"))
        {
            string line;
            while ((line = sr.ReadLine()) != null)
            {
                Word w = new Word(line);
                Add(w);
                wordList.Add(w);
            }
        }

        foreach (Word word in wordList)
        {
            Shiritori(word);
        }

        Console.WriteLine("Finish");
        Console.Read();
    }

    private static void Shiritori(Word word)
    {
        word.Used = true;
        ++count;

        if (wordDic.ContainsKey(word.Last()))
        {
            foreach (Word t2 in wordDic[word.Last()])
            {
                if (t2.Used == false)
                {
                    Shiritori(t2);
                }
            }
        }

        SetCount(count);
        --count;
        word.Used = false;
    }

    private static void SetCount(int count)
    {
        if (maxcount < count)
        {
            maxcount = count;
            Console.WriteLine(maxcount);
        }
    }
}