#include <iostream>
#include <cmath>
//using namespace std;
typedef unsigned long long ul;
typedef signed long long ll;

int main(void)
{
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  std::cout << std::fixed;
  int c, ri, ro;
  std::cin >> c >> ri >> ro;
  std::cout << (ro+ri) * (ro-ri) * (ro-ri) * M_PI * M_PI / 4.0 * c << std::endl;
  return 0;
}