Strings & Regular Expressions - 06. Email Statistics

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace _10b_Regular_Expressions_RegEx_Exercises
{
    class Regular_Expressions_RegEx_Exercises
    {
      static void Main(string[] args)
        {
            int count = int.Parse(Console.ReadLine());
            Dictionary<string, List<string>> mailList = new Dictionary<string, List<string>>();

            for (int i = 0; i < count; i++)
            {
                string pattern = @"^(?<username>[a-zA-Z]{5,})@(?<domain>(?<mailServer>[a-z]{3,})(?<topDomain>\.com|\.bg|\.org))$";
                string mail = Console.ReadLine();
                Match match = Regex.Match(mail, pattern);

                if (match.Success)
                {
                    string mailServer = match.Groups["domain"].Value;
                    string user = match.Groups["username"].Value;

                    if (!mailList.ContainsKey(mailServer))
                    {
                        mailList[mailServer] = new List<string>();
                    }
                    if (!mailList[mailServer].Contains(user))
                    {
                        mailList[mailServer].Add(user);
                    }
                }
            }

            foreach (var item in mailList.OrderByDescending(x => x.Value.Count))
            {
                  Console.WriteLine($"{item.Key}:");
                    foreach (var item2 in item.Value)
                    {
                        Console.WriteLine($"### {item2}");
                    }
            }
        }
    }
}