using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Number: " + ConvertMifareCardNumberToCardId(253490750));

    }

    public static long ConvertMifareCardNumberToCardId(long number)

    {

        try

        {

            var cardMifare = number.ToString("X4");

            var invertido = LittleEndian(cardMifare);

            var convertido = Convert.ToInt64(invertido, 16);

​

            return convertido;

        }

        catch

        {

            return 0;

        }

    }

    public static string LittleEndian(string num)

    {

        int number = Convert.ToInt32(num, 16);

        byte[] bytes = BitConverter.GetBytes(number);

        string retval = "";

        foreach (byte b in bytes)

        {

            retval += b.ToString("X2");

        }

​

        return retval;

    }

}