#include <iostream>
#include <math.h>
#include <stdio.h>
using namespace std;

int main(){
  double n,a,b;
  cin >> n >> a >> b;
  double r=(b-a)/2;
  double R=r+a;
  printf("%lf\n",2*M_PI*M_PI*r*r*R*n);
  return 0;
}