#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  double ax, bx;  // -1 <= ax < bx <= 1;
  cin >> ax >> bx;

  double ay = sqrt(1 - ax * ax);
  double by = sqrt(1 - bx * bx);

  double atheta = atan2(ay, ax);
  double btheta = atan2(by, bx);
  
  double ret = 0.0;
  if (ax >= 0)
    ret += 2 * PI * (sin(atheta) - sin(btheta));
  else if (bx <= 0)
    ret += 2 * PI * (sin(btheta) - sin(atheta));
  else
    ret += 2 * PI * (2 - sin(atheta) - sin(btheta));
  
  cout << fixed << setprecision(12) << ret << endl;
  
  return 0;
}