#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>

using namespace std;

#define M_PI 3.14159265359

int main(){
	int c;
	cin >> c;
	int r_in, r_out;
	cin >> r_in >> r_out;

	double R = (r_out-r_in)*0.5;
	double g = (r_out+r_in)*0.5;

	double S = R * R * M_PI;
	double v = g * 2 * M_PI * S;

	double ans = v*c;

	printf("%.7f\n", ans);
	return 0;
}