#include <bits/stdc++.h>
using namespace std;
const int N = 300005;
int n, l[N], r[N], p[N], a[N];
double ans, L, R, z;
bool cmp(const int i, const int j) { return a[i] < a[j]; }
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i)
    scanf("%d", a + i), p[i] = i, l[i] = i - 1, r[i] = i + 1;
  sort(p + 1, p + n + 1, cmp);
  for (int k = 1; k <= n; ++k) {
    int i = p[k], x = i, y = i;
    z = 1, L = R = 0;
    for (int c = 1; c <= 45; ++c) {
      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 * a[i] / 2;
  }
  printf("%.9lf\n", ans / n / n);
  return 0;
}
