#include <bits/stdc++.h>
using namespace std;
const int N = 300005;
const int inf = 1e9 + 7;
int a[N], pos[N];
int pre[N], nxt[N];
inline bool cmp(const int &x, const int &y) { return a[x] < a[y]; }
int main() {
  int n;
  scanf("%d", &n);
  for (int i = (1); i <= (n); i++)
    pos[i] = i, pre[i] = i - 1, nxt[i] = i + 1, scanf("%d", &a[i]);
  sort(pos + 1, pos + 1 + n, cmp);
  double ans = 0.0;
  for (int i = (1); i <= (n); i++) {
    int l = pos[i], r = pos[i];
    double s1 = 0, s2 = 0, coe = 1.0;
    for (int j = (1); j <= (50); j++) {
      if (l) s1 += 1.0 * (l - pre[l]) * coe, l = pre[l];
      if (r <= n) s2 += 1.0 * (nxt[r] - r) * coe, r = nxt[r];
      coe *= 0.5;
    }
    ans += s1 * s2 * (double)a[pos[i]];
    pre[nxt[pos[i]]] = pre[pos[i]];
    nxt[pre[pos[i]]] = nxt[pos[i]];
  }
  printf("%.12lf\n", ans / (double)n / (double)n / 2.0);
  return 0;
}
