using System;

using System.Text.RegularExpressions;

using System.Net.Mail;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var cardNumber = "333";

        Console.WriteLine(Math.Max(0, cardNumber.Length - Math.Max(0, 4)));

        cardNumber.Substring(Math.Max(0, cardNumber.Length - Math.Max(0, 4)));

        Console.WriteLine("output" + cardNumber);

    }

​

}