static void Main(string[] args)
        {
            TimerManager time = new TimerManager();
            AlarmClock alarm = new AlarmClock();
            Siren siren = new Siren();
            
            alarm.Register(time);
            time.Countdown(7);
            time.Countdown(7);
            alarm.UnRegister(time);
            time.Countdown(7);
            siren.Register(time);
            time.Countdown(4);
            siren.UnRegister(time);

            Console.ReadKey();
        }