c#

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Foulder_Counter
{
    class Program
    {
        class Month
        {
            public string name = "";
            public Dictionary<string, Day> dict_days = new Dictionary<string, Day>();

            public Month(string name)
            {
                this.name = name;
            }
        }

        class Day
        {
            public string name = "";
            public List<string> files = new List<string>();

            public Day(string name)
            {
                this.name = name;
            }
        }

        static void Main(string[] args)
        {
            Dictionary<string, Month> dict_month = new Dictionary<string, Month>();

            string path = @"C:\Users\Egor\Desktop\m4a\test";
            string[] files = Directory.GetFiles(path);

            foreach (string file in files)
            {
                string month = file.Substring(36,2);
                string day = file.Substring(39, 2);

                while (true)
                {
                    if (dict_month.ContainsKey(month))
                    {
                        if (dict_month[month].dict_days.ContainsKey(day)) { break; }
                        else { dict_month[month].dict_days.Add(day, new Day(day)); break; }
                    }
                    else dict_month.Add(month, new Month(month));

                }

                dict_month[month].dict_days[day].files.Add(file);

            }

            foreach (KeyValuePair<string, Month> m in dict_month)
            {
                Console.WriteLine("Month: {0}", m.Key);
                foreach (KeyValuePair<string, Day> d in m.Value.dict_days)
                {
                    Console.WriteLine("\tDay: {0}", d.Key);
                    foreach (string f in d.Value.files)
                    {
                        Console.WriteLine(f);
                    }
                }
            }

            Console.ReadLine();
        }
    }
}