using System;

using System.Collections;

using System.Collections.Generic;

using System.Text.RegularExpressions;

public class Program

{

    private const string CodeChars = "123456789ABCDEFGHIJKLMNPQRSTWXYZ";

    private static readonly Dictionary<char, int> CharToValue = new Dictionary<char, int>();

    public static void Main()

    {

        for (var i = 0; i<CodeChars.Length; i++)

            {

                CharToValue[CodeChars[i]] = i;

            }

            string code = "BY5Q5";

            var codeValuePart = code.Substring(0, code.Length - 1);

        Console.WriteLine(codeValuePart);

            var val = 0;

            for (var i = codeValuePart.Length - 1; i >= 0; i--)

            {

                Console.WriteLine(CharToValue[codeValuePart[i]] + " * " + Math.Pow(CodeChars.Length, codeValuePart.Length-(i+1)));

                //Console.WriteLine(codeValuePart.Length-(i+1));

                //Console.WriteLine(Math.Pow(CodeChars.Length, codeValuePart.Length-(i+1)));

                val += CharToValue[codeValuePart[i]] * (int)(Math.Pow(CodeChars.Length, codeValuePart.Length-(i+1)));

            }

        Console.WriteLine(code + " = " + val);

​

    }

}