#include <bits/stdc++.h>
using namespace std;
int b[300010], p[300010], l[300010], r[300010];
bool cmp(int i, int j) { return b[i] < b[j]; }
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &b[i]);
    p[i] = i;
    l[i] = i - 1;
    r[i] = i + 1;
  }
  sort(p + 1, p + n + 1, cmp);
  double ans = 0;
  for (int k = 1; k <= n; k++) {
    int i = p[k], x = i, y = i;
    double z = 1, L = 0, R = 0;
    for (int j = 1; j <= 45; j++) {
      if (x) {
        L += (x - l[x]) * z;
        x = l[x];
      }
      if (y <= n) {
        R += (r[y] - y) * z;
        y = r[y];
      }
      z /= 2;
    }
    l[r[i]] = l[i];
    r[l[i]] = r[i];
    ans += L * R * b[i] / 2;
  }
  printf("%.6lf\n", ans / n / n);
}
