#include <bits/stdc++.h>

using namespace std;

const double PI = acos(-1);

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

  double a, b;
  cin >> a >> b;
  double ret = 2 * PI * (b - a);
  cout << fixed << setprecision(12) << ret << endl;
  
  return 0;
}