using System;

using System.Collections.Concurrent;

public class Program

{

    public static void Main()

    {

        var cache = new ConcurrentDictionary<DateTime, string>();

        var old = DateTime.UtcNow.AddHours(-3);

        cache.TryAdd((DateTime.Now.AddHours(-2)), "x");

        cache.TryAdd((DateTime.Now.AddHours(-4)), "y");

        cache.TryAdd((DateTime.Now.AddHours(-6)), "z");

        Console.WriteLine("Original values:");

        foreach(var kvp in cache)

        {

            Console.WriteLine(kvp.Value);

        }

        foreach (var kvp in cache)

        {

            if (kvp.Key <= old)

            {

                string v;

                cache.TryRemove(kvp.Key, out v);

                Console.WriteLine(string.Format("Deleted value: {0}", v));

            }

        }

        Console.WriteLine("Remaining values:");

        foreach(var kvp in cache)

        {

            Console.WriteLine(kvp.Value);

        }

    }

}