#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
constexpr double pi = acos(-1.0);

int main() {
    int C;
    cin >> C;
    double Ri, Ro;
    cin >> Ri >> Ro;
    double r = (Ro-Ri)/2;
    cout << fixed << setprecision(10) << pi*(Ri+Ro)*r*r*pi * C << endl;
}