abstract class Shape {

    abstract double calculateArea();
}

class Square extends Shape {

    private double side;

    public Square(double side) {
        this.side = side;
    }

    double calculateArea() {
        return side * side;
    }
}

class Triangle extends Shape {

    private double base;
    private double height;

    public Triangle(double base, double height) {
        this.base = base;
        this.height = height;
    }

    double calculateArea() {
        return 0.5 * base * height;
    }
}

public class SquareTriangle {

    public static void main(String[] args) {
        Square square = new Square(5);
        Triangle triangle = new Triangle(4, 6);

        System.out.println(
            "Area of square: " + square.calculateArea() + " square units"
        );
        System.out.println(
            "Area of triangle: " + triangle.calculateArea() + " square units"
        );
    }
}
