#include <bits/stdc++.h>
using namespace std;
const int inf = 1000000007;
const long long linf = 1LL << 62;
const unsigned long long ulinf = 1ULL << 63;
const double eps = 0.000001;
const double pi = 3.14159265358979323846;
template <class T>
T abs(T a) {
  return a >= 0 ? a : -a;
}
template <class T>
T sqr(T a) {
  return a * a;
}
template <class T>
T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
template <class T>
T mod(T a, T b) {
  return (a % b + b) % b;
}
template <class T>
T addmod(T a, T b, T c) {
  return (T)mod((long long)a + b, (long long)c);
}
template <class T>
T mulmod(T a, T b, T c) {
  return (T)mod((long long)a * b, (long long)c);
}
template <class T>
T powmod(T a, T b, T c) {
  return (T)mod(
      b ? mulmod(mod(sqr((long long)powmod(a, b >> 1, c)), (long long)c),
                 (b & 1LL) ? a : 1LL, (long long)c)
        : 1LL,
      (long long)c);
}
template <class T>
void maxe(T &a, T b) {
  a = max(a, b);
}
template <class T>
void mine(T &a, T b) {
  a = min(a, b);
}
template <class T>
void mode(T &a, T b) {
  a = mod(a, b);
}
template <class T>
void addmode(T &a, T b, T c) {
  a = addmod(a, b, c);
}
template <class T>
void mulmode(T &a, T b, T c) {
  a = mulmod(a, b, c);
}
template <class T>
void powmode(T &a, T b, T c) {
  a = powmod(a, b, c);
}
int iszero(double a) { return abs(a) <= eps; }
template <class T>
void geti(T &a) {
  a = 0;
  long long b = 1;
  char c = getchar();
  if (c == '-')
    b = -1;
  else
    a = c - 48;
  while ((c = getchar()) != ' ' && c != '\n') a = a * 10 + c - 48;
  a *= b;
}
void fileio_in_out() {
  freopen(".in", "r", stdin);
  freopen(".out", "w", stdout);
}
void fileio_txt() {
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
}
const int N = 1111111;
const int M = 1111111;
int test;
long long n, m, k;
double ans;
long long x, y;
double r;
int main() {
  scanf("%I64d%lf", &n, &r);
  x = 2;
  for (long long i = 1; i < n; i++) {
    x += 2 * i * i - 2 * i + 6;
    y += 4 * i - 2;
  }
  ans = (x + y * sqrt(2)) * r / (n * n);
  printf("%.10lf\n", ans);
  return 0;
}
