#include <iostream>
#include <iomanip>
using namespace std;

const double EPS = 1e-6;
const double PI = 3.141592653589793238463;

int main() {
    int C;
    double Rin, Rout;
    cin >> C >> Rin >> Rout;

    double r = (Rout - Rin) / 2;
    double R = Rin + r;

    cout << fixed << setprecision(6)
         << 2 * PI * PI * R * r * r * C
         << endl;

    return 0;
}