#include <bits/stdc++.h>
using namespace std;
const long long inf = 1 << 30;
long long m, r;
signed main() {
  double ans = 0;
  scanf("%d%d", &m, &r);
  for (long long i = 1; i <= m; i++) {
    double sum = 2 * r;
    if (i - 1 != 0) {
      sum += 2 * r + sqrt(2) * r;
      if (i - 1 >= 2) {
        sum += r * (i - 1) * (i - 2) + (i - 2) * 2 * sqrt(2) * r;
      }
    }
    if (m - i != 0) {
      sum += 2 * r + sqrt(2) * r;
      if (m - i >= 2) {
        sum += r * (m - i - 0) * (m - i - 1) + (m - i - 1) * 2 * sqrt(2) * r;
      }
    }
    ans += sum;
  }
  printf("%.8f\n", ans / (m * m));
  return 0;
}
