/* -*- coding: utf-8 -*-
 *
 * 605.cc: No.605 板挟みの球面 - 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 */

// dS = 2PI*RcosT*RdT = 2PI*R^2*cosTdT

int main() {
  double a, b;
  scanf("%lf%lf", &a, &b);

  double sa = PI * 2 * a;
  double sb = PI * 2 * b;
  //printf("sa=%lf, sb=%lf\n", sa, sb);
  printf("%.8lf\n", sb - sa);
  return 0;
}