RealPath.cs

using System;
using System.IO;

namespace RealPath
{
    class Program
    {
        static string RealPath(string path)
        {
            if (!File.Exists(path) && !Directory.Exists(path)) return path;

            var infos = new DirectoryInfo(path);

            if (infos.Parent is null) return infos.Name.ToUpper();

            var basename = infos.Parent.GetFileSystemInfos(infos.Name)[0].Name;
            return Path.Combine(RealPath(infos.Parent.FullName), basename);
        }

        static void Main(string[] args)
        {
            foreach (string path in args)
            {
                Console.WriteLine(RealPath(path));
            }
        }
    }
}