#include <iostream>
using namespace std;
#define PI 3.141592

int main() {
  int c, r1, r2;
  cin >> c >> r1 >> r2;
  double r3 = (r2 - r1) / 2.0;
  double res = r3 * r3 * PI * 2 * PI * (r1 + r3) / c;
  cout << res << endl;
  return 0;
}