/* -*- coding: utf-8 -*-
 *
 * 89.cc: No.89 どんどんドーナツどーんといこう! - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const double PI = acos(-1.0);

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  int c, ri, ro;
  cin >> c >> ri >> ro;

  double r0 = (double)(ro - ri) / 2;
  double r1 = ri + r0;
  double v = (PI * r0 * r0) * (2.0 * PI * r1);

  printf("%.10lf\n", v * c);
  
  return 0;
}