using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(ValidateFin("A1BS31Z0430336179"));

        Console.WriteLine(ValidateFin("0Ly341Ü59810ΙX"));

    }

    private static string ValidateFin(string fin)

    {

        var multiplicator = 2;

        var finLength = fin.Length - 1;

        var sum = 0;

        for (var i = finLength; i >= 0; i--)

        {

            Console.Write(fin[i] + "-" + GetNumber(fin[i]) + "-" + (GetNumber(fin[i]) * multiplicator) + "|");

            sum += GetNumber(fin[i]) * multiplicator;

            if (multiplicator == 10)

            {

                multiplicator = 2;

            }

            else

            {

                multiplicator++;

            }

        }       

        var output = sum % 11;

        return output == 10 ? "X" : output.ToString();

    }

    private static int GetNumber(char c)

    {

        // keep numbers

        if (Char.IsDigit(c)) return (int)(c - '0');

        // convert special characters and transform to upper

        c = ConvertSpecialCharacters(c);

        // calculate

        var output = ((c - 64) % 9);

        // after r we have to increase output by 1

        output += ((int)c <= ((int)'R')) ? 0 : 1;

        // there is no 0

        return output == 0 ? 9 : output;

    }

    private static char ConvertSpecialCharacters(char c)

    {

        switch (Char.ToUpper(c))

        {

            case 'Ö':

                return 'O';

            case 'Ä':

                return 'A';

            case 'Ü':

                return 'U';

            // roman numbers to letters

            case 'Ι':

                return 'I';

            // V, X, L, D, M are missing yet

            default:

                return Char.ToUpper(c);

        }

    }

}