#include <stdio.h>

int main(){
  // ２π² ｒ² Ｒ
  int c,ri,ro;
  double r, R;
  double pi = 3.1415926535897932;

  scanf("%d%d%d", &c,&ri,&ro);
  r = (ro - ri) / 2.0;
  R = ri + r;
  printf("%lf\n", 2 * pi * pi * r * r * R * c);
  return 0;
}