Chat Logger

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

public class ChatLogger
{
    public static void Main()
    {
        DateTime today = DateTime.ParseExact(
            Console.ReadLine(),
            "dd-MM-yyyy HH:mm:ss",
            CultureInfo.InvariantCulture);

        var messages = new SortedDictionary<DateTime, string>();

        string input = Console.ReadLine();

        while (input != "END")
        {
            string[] tokens = Regex.Split(input, @"\s+\/\s+");

            string message = tokens[0];
            DateTime date = DateTime.ParseExact(
            tokens[1],
            "dd-MM-yyyy HH:mm:ss",
            CultureInfo.InvariantCulture);

            messages.Add(date, message);

            input = Console.ReadLine();
        }

        foreach (var message in messages)
        {
            Console.WriteLine("<div>{0}</div>", SecurityElement.Escape(message.Value));
        }

        var mostRecentPostDate = messages.Last().Key;
        string time = string.Empty;

        var difference = (today - mostRecentPostDate);

        if (mostRecentPostDate.AddDays(1).Date == today.Date)
        {
            time = "yesterday";
        }
        else if (difference.TotalDays > 1)
        {
            time = string.Format("{0:dd-MM-yyyy}", mostRecentPostDate);
        }
        else
        {
            var seconds = (int)difference.TotalSeconds;

            if (seconds < 60)
            {
                time = "a few moments ago";
            }
            else if (seconds < 60 * 60)
            {
                time = string.Format(
                    "{0} minute(s) ago",
                    (int)difference.TotalMinutes);
            }
            else
            {
                time = string.Format(
                    "{0} hour(s) ago",
                    (int)difference.TotalHours);
            }
        }

        Console.WriteLine("<p>Last active: <time>{0}</time></p>", time);
    }
}