class Pizza {
    
    // The area (in sq.in.) of a pizza, whose diameter is `diam` (in inches)
    // diam must be non-negative.
    static double pizzaArea( double diam ) {
        return Math.pow(diam/2, 2) * Math.PI;
        }
    
    
    
    static void testPizzaArea() {
        assert pizzaArea(20) == 100 * Math.PI;
        assert pizzaArea(2) == Math.PI;
        assert pizzaArea(0) == 0;
        assert pizzaArea(2.5) == 4.908738521234052;
    }
    
    
}