static void Main(string[] args)
        {
            MotorBike myBike = new MotorBike(new GasEngine(100));

            myBike.SetSpeed(90);
            Console.WriteLine("Current speed is: " + myBike.CurrentSpeed().ToString());
            myBike.RunAtHalfSpeed();
            Console.WriteLine("Current speed is: " + myBike.CurrentSpeed().ToString());
            Console.ReadLine();
        }