        static void Main(string[] args)
        {
            Circle circle1 = new Circle(72, 22, 4.5);
            Circle circle2 = new Circle(5, 5, 10);
            Console.WriteLine();
            Console.WriteLine("Area is : {0}", circle1.Area());
            Console.WriteLine ("Perimeter is : {0}", circle1.Circumference());
            Console.WriteLine();
            circle1 = null;
            circle2 = null;
            GC.Collect();
            Console.Read();
        }
