#include <bits/stdc++.h>
using namespace std;
const int MAXN = 300300;
const int MAX = 70;
int b[MAXN];
int main(void) {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < (n); ++i) scanf("%d", b + i);
  static pair<int, int> a[MAXN];
  for (int i = 0; i < (n); ++i) a[i] = {b[i], i};
  sort(a, a + n, greater<pair<int, int> >());
  static set<int> S;
  double ans = 0;
  for (int i = 0; i < (n); ++i) {
    int x = a[i].first, pos = a[i].second;
    auto it = S.lower_bound(pos);
    static int l[MAX];
    int nl = 0;
    auto itl = it;
    while (nl < MAX && itl != S.begin()) l[nl++] = *(--itl);
    int last = pos;
    for (int i = 0; i < (nl); ++i) l[i] = last - l[i], last -= l[i];
    if (nl < MAX) l[nl++] = last - 0 + 1;
    static int r[MAX];
    int nr = 0;
    auto itr = it;
    while (nr < MAX && itr != S.end()) r[nr++] = *(itr++);
    last = pos;
    for (int i = 0; i < (nr); ++i) r[i] = r[i] - last, last += r[i];
    if (nr < MAX) r[nr++] = n - last;
    double suml = 0, p2 = 1;
    for (int i = 0; i < (nl); ++i) suml += l[i] / p2, p2 *= 2;
    double sumr = 0;
    p2 = 1;
    for (int i = 0; i < (nr); ++i) sumr += r[i] / p2, p2 *= 2;
    ans += suml * sumr * x / 2.0 / n;
    S.insert(pos);
  }
  ans /= n;
  printf("%lf\n", ans);
  return 0;
}
