static void Main(string[] args)
        {
            GSM phone       = new GSM("lala", "sumsAng", "batman", 10000.99);
            GSM secondPhone = new GSM("lol", "krusha", "suparMan", 9999,
                                      new Battery("tuhla", 2, 1), new Display(5.5, 3));

            Console.WriteLine(phone.ToString());
            Console.WriteLine(secondPhone.ToString());
        }
        static void Main(string[] args)
        {
            GSM phone = new GSM("lala", "sumsAng", "batman", 10000.99);
            GSM secondPhone = new GSM("lol", "krusha", "suparMan", 9999,
                new Battery("tuhla", 2, 1), new Display(5.5, 3));

            Console.WriteLine(phone.ToString());
            Console.WriteLine(secondPhone.ToString());
        }