#include <bits/stdc++.h>

using namespace std;

const double pi = acos(-1);

int main(void) {
  int c, Ri, Ro;
  cin >> c >> Ri >> Ro;
  
  double r = (Ro - Ri) / 2.0;
  printf("%.10f\n", pi * r * r * 2 * pi * (Ri + r) * c);

  return 0;
}