public class Rectangle implements Polygon
{
    private double width;
    private double height;
    public Rectangle(double width, double height)
    {
        this.width = width;
        this.height = height;
    }
    public double perimeter()
    {
        return 2*(width + height);
    }
    public double area()
    {
        return width*height;
    }
    public double diameter()
    {
        return Math.hypot(width, height);
    }
    public int numSides()
    {
        return 4;
    }
}