#define _USE_MATH_DEFINES
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <iomanip>
#include <functional>
#include <cmath>
#include <math.h>
using namespace std;
#define lli long long int

int main() {
	int c;
	int in, out;
	double futosa, r2;
	cin >> c >> in >> out;
	futosa = (out - in) / 2.0;
	r2 = (out + in);
	cout << fixed << setprecision(10) << r2 * M_PI * pow(futosa, 2) * M_PI * c << endl;;
	return 0;
}