using System;

public class BelgiumTaxIdentificationNumber

{

    public static void Main()

    {

        bool isValid = isValidBTIN("00012511148");

        Console.WriteLine(isValid);

    }

    private static bool authenticateMonth(int month)

    {

        if (month > 12)

        {

            return false;

        }

        return true;

    }

    private static bool authenticateDate(int date)

    {

        if (date > 31)

        {

            return false;

        }

        return true;

    }

    private static bool authenticateBTIN(string btin, int key)

    {

        int answer = 97 - Convert.ToInt32(btin) % 97;

        if (answer != key)

        {

            answer = 97 - Convert.ToInt32(string.Concat("2",btin)) % 97;

            if (answer != key) return false;

        }

        return true;

    }

    private static bool isValidBTIN(string btin)

    {

        if (btin.Length != 11) return false;

        int month = Convert.ToInt32(btin.Substring(2,2));

        if (!authenticateMonth(month)) return false;

        int date = Convert.ToInt32(btin.Substring(4,2));

        if (!authenticateDate(date)) return false;

        int wholestring_check = Convert.ToInt32(btin.Substring(9, 2));

        string wholestring = btin.Substring(0, btin.Length - 2);

​

        if (!authenticateBTIN(wholestring, wholestring_check)) return false;

        return true;

    }

}