using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var lastHeardFrom = new Dictionary<string, DateTime>();

        int HandlerTimeToLiveMinutes = 15;

        var firstList = new List<string>(){"1","2","3"};

        var secondList = new List<string>(){"3","4","5"};

        var thirdList = new List<string>() {"1","3","7"};

        var fourthList = new List<string>(){"6","7","8","10"};

        var listToClean = firstList.Union(secondList).Union(thirdList).Union(fourthList).ToList();

        listToClean.ForEach(i =>

            {

                Console.WriteLine(i);

                if (lastHeardFrom.ContainsKey(i))

                {

                    if ((DateTime.Now - lastHeardFrom[i]).TotalMinutes >= HandlerTimeToLiveMinutes)

                    {

                        // CleanUpHandler(i);

                    }

                }

            });

    }

}