#include <bits/stdc++.h>

using namespace std;

#define PI acos(-1.0)

int main() {
    double c, Rin, Rout;
    cin >> c >> Rin >> Rout;
    double R1 = (Rin + Rout) / 2.0, R2 = (Rout - Rin) / 2.0;
    double v = PI * R2 * R2 * 2.0 * PI * R1;

    cout << fixed << setprecision(6);
    cout << c * v << endl;
    return 0;
}