// No.89 どんどんドーナツどーんといこう！
// https://yukicoder.me/problems/no/89
//
#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    int C;
    cin >> C;
    int Rin, Rout;
    cin >> Rin >> Rout;
    double R = (Rin + Rout) / 2.0;
    double r = Rout - R;
    double V = 2 * pow(M_PI, 2) * pow(r, 2) * R;
    double ans = V * C;
    cout << fixed << setprecision(10) << ans << endl;
}