static void Main(string[] args)
        {
            {
                Console.WriteLine("Overriding Method Example");
                var shapes = new List <Shape>();
                shapes.Add(new Circle());
                shapes.Add(new Rectangle());
                shapes.Add(new Triangle());

                var canvas = new Canvas();
                canvas.DrawShapes(shapes);

                Console.WriteLine("=================");
                Console.WriteLine("Abstract Class Example");
                var circle = new Circles();
                circle.Draw();

                var rectangle = new Rectangles();
                rectangle.Draw();
            }
        }