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

int main() {
  int C, R_in, R_out;
  cin >> C >> R_in >> R_out;
  const double PI = acos(-1);
  cout << fixed
       << C * 2 * PI * PI * ((R_in + R_out) / 2.0) * ((R_out - R_in) / 2.0) *
              ((R_out - R_in) / 2.0)
       << endl;
}