#include <iostream>
using namespace std;

const int PI = 3.1415926535;


class Figure {
public:
    virtual double Area() const = 0;
};

class Square : public Figure {
private:
    double a;
public:
    Square(double a): a(a) {}
    double Area() const {
        return a * a;
    }
};

class Circle : public Figure {
private:
    double r;
public:
    Circle(double r): r(r) {}
    double Area() const {
        return PI * r * r;
    }
};