#include <stdio.h>
#include <math.h>

int main(void)
{
  int C, Rin, Rout;
  double pi, R, r;
  
  scanf("%d", &C);
  scanf("%d %d", &Rin, &Rout);

  pi = acos(-1);
  r = (double)(Rout - Rin) / 2;
  R = r + Rin;

  printf("%lf\n", 2 * pi * pi * R * r * r * C);

  return 0;
}