#include <stdio.h>
#include <math.h>
#define PI 3.14159265358979323846

int main() {
  int c, rin, rout;
  scanf("%d %d %d", &c, &rin, &rout);

  printf("%0.8lf", pow(PI, 2)*(rin+rout)*pow(rout-rin, 2)/4*c);
  return 0;
}