// コピーして使う！
#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
    double c, rin, rout;
    cin >> c >> rin >> rout;
    double radius = 2*((rout-rin)/2+rin) * M_PI;
    double area = pow(((rout - rin) / 2), 2) * M_PI;
    double ans = c * area * radius;

    cout << fixed << setprecision(20);
    // cout << radius << endl;
    // cout << area << endl;
    cout << ans << endl;

    system("pause");
}