#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
const double pi = atan(1.0) * 4.0;

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