#include <iostream>
#include <iomanip>
using namespace std;

#define PI 3.1415926
#define pTwo(x) x*x

struct Circle{
	double radius;
};

struct Ring{
	Circle c1, c2;
}ring;

double area(Ring ring){
	return PI*pTwo(ring.c2.radius) - PI*pTwo(ring.c1.radius);
}

int main(){
	double startX, startY, smallRadius, largeRadius;
	while(cin >> startX >> startY >> largeRadius >> smallRadius){
		ring.c1.radius = smallRadius;
		ring.c2.radius = largeRadius;
		cout << fixed << setprecision(6) << "Area: " << area(ring) << endl;
	}
	return 0;
}