using System;

using System.Text;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("isIban");

        Console.WriteLine(Program.IsIban("NL92RABO0174302258").ToString());

    }

        private static bool IsIban(string value) {

            if (string.IsNullOrEmpty(value) || value.Length < 5) {

                return false;

            }

            var bankAccount = value.ToUpper(); // In order to cope with the regex below

            if (Regex.IsMatch(bankAccount, "^[A-Z0-9]")) {

                bankAccount = bankAccount.Replace(" ", String.Empty).Replace("-", string.Empty);

                string bank = bankAccount.Substring(4, bankAccount.Length - 4) + bankAccount.Substring(0, 4);

                int asciiShift = 55;

                StringBuilder sb = new StringBuilder();

                foreach (char c in bank) {

                    int v;

                    if (char.IsLetter(c)) {

                        v = c - asciiShift;

                    }

                    else {

                        v = int.Parse(c.ToString());

                    }

                    sb.Append(v);

                }

                string checkSumString = sb.ToString();

                int checksum = int.Parse(checkSumString.Substring(0, 1));

                for (int i = 1; i < checkSumString.Length; i++) {

                    int v = int.Parse(checkSumString.Substring(i, 1));

                    checksum *= 10;

                    checksum += v;

                    checksum %= 97;

                }

                return checksum == 1;

            }

            else {

                return false;

            }

        }

}