#include <bits/stdc++.h>
using namespace std;
const long long INF = 1LL << 60;
long long powmod(long long a, long long b) {
  long long res = 1;
  a %= 1000000007;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % 1000000007;
    a = a * a % 1000000007;
  }
  return res;
}
template <typename T>
inline bool chkmin(T &a, const T &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T>
inline bool chkmax(T &a, const T &b) {
  return a < b ? a = b, 1 : 0;
}
int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
int a[310000], p[310000], l[310000], r[310000];
bool cmp(int i, int j) { return a[i] < a[j]; }
int main() {
  int n = read();
  for (int i = 1; i <= n; i++) {
    a[i] = read();
    p[i] = i;
    l[i] = i - 1;
    r[i] = i + 1;
  }
  sort(p + 1, p + 1 + n, cmp);
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double L = 0, R = 0;
    int x = p[i];
    double y = 1;
    int ll = x, rr = x;
    for (int _ = 0; _ < 50; _++) {
      if (ll) L += (ll - l[ll]) * y, ll = l[ll];
      if (rr <= n) R += (r[rr] - rr) * y, rr = r[rr];
      y /= 2.0;
    }
    r[l[x]] = r[x];
    l[r[x]] = l[x];
    ans += L * R * a[x] / 2.0;
  }
  printf("%.10lf", ans / n / n);
  return 0;
}
