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

int main()
{
  int c;
  int Rin;
  int Rout;
  double taiseki;
  double enshu;
  double menseki;
  double cal;
  scanf("%d %d %d",&c,&Rin,&Rout);


  //ドーナツを切った時の面積
  //x = pi * (Rout-Rin)^2
  //ドーナツの体積
  //(Rout - Rin)/2 *x
  menseki = M_PI*(double)(Rout-Rin)*(double)(Rout-Rin)/4.0;
  enshu   = (double)(Rin +(double)(Rout-Rin)/2.0)*2.0*M_PI;
  taiseki = menseki * enshu;
  cal     = taiseki*c;

  //printf("menseki = %f\n",menseki);
  //printf("enshu   = %f\n",enshu);
  //printf("taiseki = %f\n",taiseki);
  printf("%f\n",cal);

  return 0;
}