using System;

using System.Text.RegularExpressions;

public class Path

{

 public string CurrentPath { get; private set; }

 public Path(string path)

 {

 this.CurrentPath = path;

 }

 public Path Cd(string newPath)

 {

 //throw new NotImplementedException("Waiting to be implemented."); 

     var lastOccurance = this.CurrentPath.LastIndexOf('/');

     var req = this.CurrentPath.Substring(0,(lastOccurance+1));

     return new Path(req + newPath.Substring(3));

 }

 public static void Main(string[] args)

 {

     ChangeDirectory();

 }

 private static void ChangeDirectory()

 {

   Console.WriteLine("Enter the directory path");

   string inputPath = Console.ReadLine();

   bool match = Regex.IsMatch(inputPath, @"^[a-zA-Z/]+$");

   if(!match)

   {

    Console.WriteLine("Sorry, Directory names consist only of English alphabet letters (A-Z and a-z)");

    ChangeDirectory();

    return;

   }

   else

   {

   Path path = new Path(inputPath);

   Console.WriteLine("Enter the change directory path");

   string changePath = Console.ReadLine();  

   while(!ValidateRequestedPath(changePath))

   {

   changePath = Console.ReadLine(); 

   }

   Console.WriteLine(path.Cd(changePath).CurrentPath);

   Console.ReadLine();

   }

 }

 private static bool ValidateRequestedPath(string input)

 {

 if(!input.StartsWith(".."))

 {

     Console.WriteLine("Change directory should starts with ..");

     return false;

 }

     return true;

 }

​

}