public void Update(NumberGenerator generator)
        {
            Console.WriteLine("GraphObserver: ");

            int count = generator.Number;

            for (var i = 0; i < count; i++)
            {
                Console.Write("*");
            }
            Console.WriteLine();

            Thread.Sleep(1000);
        }
        public void Update(NumberGenerator generator)
        {
            Console.WriteLine($"DigitObserver: {generator.Number}");

            Thread.Sleep(1000);
        }