class Test {
    public static void main(String[] args) {
        Point p1 = new Point(new Number(1), new Number(2));
        Point p2 = new Point(new Number(3), new Number(4));
        Rectangle r1 = new Rectangle(p1, p2);

        Point p3 = new Point(new RationalNumber(1, 2), new RationalNumber(3, 1));
        Point p4 = new Point(new RationalNumber(3, 2), new RationalNumber(1, 1));
        Rectangle r2 = new Rectangle(p3, p4);

        System.out.println(r1.area());
        System.out.println(r2.area());
    }
}

class Rectangle {
    protected Point topLeft;
    protected Point bottomRight;

    public Rectangle(Point topLeft, Point bottomRight) {
        this.topLeft = topLeft;
        this.bottomRight = bottomRight;
    }

    public String toString() {
        return "[" + topLeft.toString() + "," + bottomRight.toString() + "]";
    }

    public Number area() {
        Number length_y = topLeft.getY().minus(bottomRight.getY()).abs();
        Number length_x = bottomRight.getX().minus(topLeft.getX()).abs();
        return length_y.times(length_x);
    }
}

class Point {
    protected Number x;
    protected Number y;

    public Point(Number x, Number y) {
        this.x = x;
        this.y = y;
    }

    public Number getX() {
        return x;
    }

    public Number getY() {
        return y;
    }

    public String toString() {
        return "(" + x.toString() + "," + y.toString() + ")";
    }
}

class Number {
    protected double value;

    public Number(double value) {
        this.value = value;
    }

    public Number minus(Number other) {
        return new Number(value - other.value);
    }

    public Number times(Number other) {
        return new Number(value * other.value);
    }

    public Number abs() {
        if (value < 0) {
            return new Number(-value);
        } else {
            return this;
        }
    }

    public String squee() {
        String s = "squee";
        for (int i = 0; i < value; i++) {
            s += "e";
        }
        return s;
    }

    public String toString() {
        return String.valueOf(value);
    }
}

/* Observe that I can EXTEND my program by only APPENDING a new
 * class for RationalNumber, and then modifying just the main
 * method.  I do not need to modify any prior code, including
 * either Point or Rectangle.  They just work!  Asymptotically,
 * instead of having to modify O(m*n) things when adding n new
 * things to a language, I only need to modify O(n).
 */
class RationalNumber extends Number {
    protected double numerator;
    protected double denominator;

    public RationalNumber(double numerator, double denominator) {
        super(numerator / denominator);
        this.numerator = numerator;
        this.denominator = denominator;
    }

    public String toString() {
        return String.valueOf(numerator) + "/" + String.valueOf(denominator);
    }
}