#include <iostream>
#include <cstdio>
using namespace std;
#define PI 3.1415926535

int main() {
  int c, r1, r2;
  cin >> c >> r1 >> r2;
  double r3 = (double)(r2 - r1) / 2;
  double res = r3 * r3 * 2 * (r1 + r3) * PI * PI * (double)c;
  printf("%.5f", res);
  return 0;
}