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

double pappus(int c,int in,int out){
  double r=(double)(out-in)*0.5;
  return c*2*M_PI*(in+r)*(M_PI*r*r);
}

void run(void){
  int c;
  scanf("%d",&c);
  int in,out;
  scanf("%d%d",&in,&out);
  double ans=pappus(c,in,out);
  printf("%.5lf\n",ans);
  return;
}

int main(void){
  run();
  return 0;
}