#include <bits/stdc++.h>
using namespace std;
double mar[100000];
int main() {
  double ml, rl;
  cin >> ml >> rl;
  double m = ml, r = rl;
  double save = 0;
  if (ml >= 3)
    save += 2 * m * (m - 3) + 2 * (m - 2) + 6;
  else if (ml == 2)
    save += 2;
  save *= (sqrt(2) - 2);
  double ans = m * (m + 1) + m * (m + 1) * (2 * m + 1) / 3 - 2 * (m);
  ans += save;
  ans *= r;
  ans /= (m * m);
  printf("%.10f\n", ans);
  return 0;
}
