using System;

public class Program

{

    public class Rootobject

    {

        public string dir { get; set; }

        public string[] files { get; set; }

        public Rootobject[] folders { get; set; }

    }

    public static int GetNumberOfFilesWithHackExt(string[] files)

    {

        int count = 0;

        foreach (string file in files)

        {

            if (file.EndsWith(".hack"))

                count++;

        }

        return count;

    }

    public static int GetNumberOfInfectedFilesRecursively(Rootobject root)

    {

        int count = 0;

        if (root.files != null)

            count += GetNumberOfFilesWithHackExt(root.files);

        if (root.folders != null)

        {

            foreach (Rootobject folder in root.folders)

            {

                count += GetNumberOfInfectedFilesRecursively(folder);

            }

        }

        return count;

    }

    public static void Main()

    {

        var root = new Rootobject()

        {

            dir = "main",

            files = new string[] { "file1.txt", "file2.hack" },

            folders = new Rootobject[]

            {

                new Rootobject()

                {

                    dir = "sub1",

                    files = new string[] { "subfile1.bat", "subfile2.json" }

                },

                new Rootobject()

                {

                    dir = "sub2",

                    files = new string[] { "subfile2.hack", "subfile2.zip" }

                }

            }

        };

        int num = GetNumberOfInfectedFilesRecursively(root);

        Console.WriteLine(num);

    }

}