#include <iostream>
#define _USE_MATH_DEFINES
#include <math.h>
using namespace std;

int main()
{
	int c, y, x;
	cin >> c >> y >> x;

	double r = 1. / 2 * (x - y);
	double R = 1. / 2 * (x + y);
	double ans = (2 * M_PI * R) * (M_PI * pow(r, 2)) * c;

	printf("%.5f\n", ans);
}