File Stream C#

using System;
using System.IO;
class MainClass {
    static void Main(string[] args) {
        DirectoryInfo dir = new DirectoryInfo("c:\\");
        Console.WriteLine("Total size: " + CalculateDirectorySize(dir, true).ToString() + " bytes.");
    }
    static long CalculateDirectorySize(DirectoryInfo directory, bool includeSubdirectories) {
        long totalSize = 0;
        FileInfo[] files = directory.GetFiles();
        foreach (FileInfo file in files) {
            totalSize += file.Length;
        }
        if (includeSubdirectories) {
            DirectoryInfo[] dirs = directory.GetDirectories();
            foreach (DirectoryInfo dir in dirs) {
                totalSize += CalculateDirectorySize(dir, true);
            }
        }
        return totalSize;
    }
}