using System;

public class Program

{

    public static void Main()

    {

        Uri path1 = new Uri(@"c:\dir1\dir2\");

        Uri path2 = new Uri(@"c:\dir1\dir3\file1.txt");

        Uri diff = path1.MakeRelativeUri(path2);

        string relPath = diff.OriginalString;

        Console.WriteLine(relPath);

    }

}