#include <cstdio>
#include <cmath>

#include <iostream>
#include <vector>
#include <list>
#include <algorithm>

int main() {

  /* default begin */
  long i, j, k;
  long n, m;
  //long temp;
  long t;
  std::vector<long> v;
  bool b;
  /* default end */

  double C, r1, r2;
  double pi = 3.14159265358979323846264338327950288419716939937510;
  double temp;

  std::cin >> C;
  std::cin >> r1 >> r2;

  temp = (r2+r1)/2-r1;

  printf("%.7lf\n", temp*temp*pi*(temp+r1)*2*pi*C);

  return 0;
}