/// <summary>
    /// The entry point of the program.
    /// </summary>
    private static void Main()
    {
        Circle circle = new Circle(5);
        Console.WriteLine(
            "I am a circle. My perimeter is {0:f2}. My area is {1:f2}.",
            circle.CalcPerimeter(),
            circle.CalcArea());

        Rectangle rectangle = new Rectangle(2, 3);
        Console.WriteLine(
            "I am a rectangle. My perimeter is {0:f2}. My surface is {1:f2}.",
            rectangle.CalcPerimeter(),
            rectangle.CalcArea());
    }