Size of Folder in Bytes (Deep or Shallow)

using System;
using System.IO;

public class Folder {
private static double sizeInBytes;

public static double Size(string directory, bool deep) {
DirectoryInfo dir = new DirectoryInfo(directory);
foreach(FileInfo f in dir.GetFiles()) {
sizeInBytes += f.Length;
}
if(deep) {
foreach(DirectoryInfo d in dir.GetDirectories()) {
Size(d.FullName, deep);
}
}
return sizeInBytes;
}

static void Main() {
Console.WriteLine("The total folder size in bytes is {0}", Folder.Size(@"c:\sonysys", true));
}
}