C# calculate disk size

    static void Main(string[] args)
        {
            string dir = @"C:\";
            string[] dirs=Directory.GetDirectories(dir);
            long totalSize = ;
            if(dirs!=null && dirs.Any())
            {
                foreach(string dr in dirs)
                {
                    var size = new DirectoryInfo(dr).GetDirectorySize();
                    totalSize += size;
                    Console.WriteLine($"dir:{dr},size:{size}");
                }
            }
            Console.WriteLine($"totalSize:{totalSize}");
            System.Diagnostics.Debug.WriteLine($"totalSize:{totalSize}");
        }  

static class DirHelper
    {
        public static long GetDirectorySize(this System.IO.DirectoryInfo directoryInfo, bool recursive = true)
        {
            var startDirectorySize = default(long);
            try
            {

                if (directoryInfo == null || !directoryInfo.Exists)
                    return startDirectorySize; //Return 0 while Directory does not exist.

                //Add size of files in the Current Directory to main size.
                foreach (var fileInfo in directoryInfo.GetFiles())
                    System.Threading.Interlocked.Add(ref startDirectorySize, fileInfo.Length);

                if (recursive) //Loop on Sub Direcotries in the Current Directory and Calculate it's files size.
                    System.Threading.Tasks.Parallel.ForEach(directoryInfo.GetDirectories(), (subDirectory) =>
                System.Threading.Interlocked.Add(ref startDirectorySize, GetDirectorySize(subDirectory, recursive)));

                  //Return full Size of this Directory.
            }
            catch
            {

            }
            return startDirectorySize;
        }
    }

static void DiskDemo()
        {
            string dir = @"C:\Windows\";
            string[] dirs = Directory.GetDirectories(dir);
            long totalSize = ;
            StringBuilder builder = new StringBuilder();
            List<Dir> dirList = new List<Dir>();
            if (dirs != null && dirs.Any())
            {
                foreach (string dr in dirs)
                {
                    var size = new DirectoryInfo(dr).GetDirectorySize();
                    Dir d = new Dir();
                    d.DirName = dr;
                    d.DirSize = size;
                    dirList.Add(d);
                    totalSize += size;
                }
            }

            foreach (var dd in dirList.OrderByDescending(x => x.DirSize))
            {
                System.Diagnostics.Debug.WriteLine(dd);
                Console.WriteLine(dd);
            }
            System.Diagnostics.Debug.WriteLine($"totalSize:{totalSize}");
        }

 class Dir
    {
        public string DirName { get; set; }
        public long DirSize { get; set; }

        public override string ToString()
        {
            return $"DirName:{DirName},DirSize:{DirSize}";
        }
    }