using System;

public class IrelandTaxIdentificationNumber

{

    public static void Main()

    {

        bool isValid = isValidITIN("1234567T");

        Console.WriteLine(isValid);

    }

    private static bool authenticateKey(string key)

    {

        char[] alphabets = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W'};

        bool flag = false;

        foreach (char ch in alphabets)

        {

            if (ch.ToString().Equals(key)) return true;

        }

        return flag;

    }

    private static bool authenticateLastDigit(string ldigit)

    {

        char[] alphabets = {'A','B','C','D','E','F','G','H','I','W'};

        bool flag = false;

        foreach (char ch in alphabets)

        {

            if (ch.ToString().Equals(ldigit)) return true;

        }

        return flag;

    }

    private static string getReminder(string itin)

    {

        char[] alphabets = {'A','B','C','D','E','F','G','H','I'};

        int addition = 0;

        for (int i=0;i<itin.Length - 1;i++)

        {

            addition += (Convert.ToInt32(itin[i]) - 48) * (itin.Length - i);

        }

        int start = 1;

​

        foreach (char ch in alphabets)

        {

            if (ch.Equals(itin[itin.Length - 1]))

            {

                addition += start * 9;

            }

            start += 1;

        }

        int answer = addition % 23;

        if (answer == 0) return "W";

        return ((char)(answer + 64)).ToString();

    }

    private static bool isValidITIN(string itin)

    {

        if (itin.Length != 8 && itin.Length != 9) return false;

        string wholestring_check = itin[7].ToString();

        if (!authenticateKey(wholestring_check)) return false;

​

        string lastdigit = itin[itin.Length - 1].ToString();

        if (!authenticateLastDigit(lastdigit)) return false;

        string wholestring = itin.Remove(itin.Length - 2,1);

        string wholestring_reminder = getReminder(wholestring);

​

        if (!wholestring_reminder.Equals(wholestring_check)) return false;

        return true;

    }

}