#include<iostream>
#include<algorithm>
#include<stdio.h>
#include<stdlib.h>
#include<vector>
#include<string>
#include<sstream>
#include<math.h>
using namespace std;


int main(){

  int c;
  cin >> c;
  int r[2];
  cin >> r[0] >> r[1];
  double tmp = (r[1]-r[0]);
  printf("%.6lf\n", 2 * M_PI * (r[0] + tmp/2) * (tmp/2)*(tmp/2) * M_PI * c );


  return 0;
}