class Shape:
    def area(self):
        return 0

class Circle(Shape):
    def __init__(self, r):
        self.r = r
    def area(self):
        return 3.14 * self.r * self.r

class Square(Shape):
    def __init__(self, side):
        self.side = side
    def area(self):
        return self.side * self.side