using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Console.WriteLine(GetIbanByAccountNumber("81280000743376001"));

    }

    private static string GetIbanByAccountNumber(string acctNo)

        {            

            if (string.IsNullOrWhiteSpace(acctNo))

                return null;

            if (acctNo.Length > 19)

                return "";

            var cc = "IR";

            var cctemp = "182700";

            var bban = $"056{acctNo.PadLeft(19, '0')}";

            var cx = decimal.Parse($"{bban}{cctemp}");

            var cdmod = cx % 97;

            var cd = 98 - cdmod;

            var sheba = decimal.Parse($"{cd}{bban}");

            return sheba.ToString("IR000000000000000000000000");

        }

}