#include <bits/stdc++.h>
using namespace std;
const int N = 333333;
int a[N];
int pos[N];
set<int> s;
int n;
bool cmp(const int pos1, const int pos2) {
  if (a[pos1] != a[pos2]) return a[pos1] > a[pos2];
  return pos1 < pos2;
}
double calc(int pos) {
  set<int>::iterator sit;
  int prev;
  double c1 = 0, c2 = 0, two;
  two = 1;
  sit = s.lower_bound(pos);
  sit--;
  for (int i = 0, prev = pos; i < 45; i++) {
    c1 += two * (prev - *sit);
    two /= 2.0;
    prev = *sit;
    if (*sit == 0) break;
    sit--;
  }
  two = 1;
  sit = s.lower_bound(pos);
  for (int i = 0, prev = pos; i < 45; i++) {
    c2 += two * (*sit - prev);
    two /= 2.0;
    prev = *sit;
    if (*sit == n + 1) break;
    sit++;
  }
  s.insert(pos);
  return c1 * c2 / 2.0;
}
void solve() {
  sort(pos + 1, pos + n + 1, cmp);
  s.insert(0);
  s.insert(n + 1);
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    ans += calc(pos[i]) * a[pos[i]];
  }
  ans = ans / n / n;
  printf("%.10f\n", ans);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    pos[i] = i;
  }
  solve();
  return 0;
}
