#include <bits/stdc++.h>

using namespace std;

const double pi = M_PI;

int main() {
	int C; cin >> C;
	int r1, r2; cin >> r1 >> r2;
	double r = (r2-r1)/2.0;
	double S = pi * r * r;
	double L = 2 * pi * (r + r1);
	cout << fixed << setprecision(10) << S * L * C << endl;
}