using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.IO;

using System.Net;

using System;

using System.Diagnostics;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string filename = "%2E%2E%2fhacking.pdf";

        Console.WriteLine("Hello Wodddrld");

        if (filename.IndexOfAny(System.IO.Path.GetInvalidFileNameChars()) != -1)

        {

            Console.WriteLine("hacked!");

        }

        string regex = @"^[a-zA-Z0-9](?:[a-zA-Z0-9 ._-]*[a-zA-Z0-9])?\.[a-zA-Z0-9_-]+$";

        Match m = Regex.Match(filename, regex, RegexOptions.IgnoreCase);

        if (m.Success)

        {

            Console.WriteLine(m.Value);

        }

        else

        {

            Console.WriteLine("hacked!");

        }

    }

}