#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void smin(T &a, const U &b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, const U &b) {
  if (a < b) a = b;
}
template <class T>
inline void gn(T &first) {
  char c, sg = 0;
  while (c = getchar(), (c > '9' || c < '0') && c != '-')
    ;
  for ((c == '-' ? sg = 1, c = getchar() : 0), first = 0; c >= '0' && c <= '9';
       c = getchar())
    first = (first << 1) + (first << 3) + c - '0';
  if (sg) first = -first;
}
template <class T1, class T2>
inline void gn(T1 &x1, T2 &x2) {
  gn(x1), gn(x2);
}
template <class T1, class T2, class T3>
inline void gn(T1 &x1, T2 &x2, T3 &x3) {
  gn(x1, x2), gn(x3);
}
template <class T1, class T2, class T3, class T4>
inline void gn(T1 &x1, T2 &x2, T3 &x3, T4 &x4) {
  gn(x1, x2, x3), gn(x4);
}
template <class T1, class T2, class T3, class T4, class T5>
inline void gn(T1 &x1, T2 &x2, T3 &x3, T4 &x4, T5 &x5) {
  gn(x1, x2, x3, x4), gn(x5);
}
template <class T>
inline void print(T first) {
  if (first < 0) {
    putchar('-');
    return print(-first);
  }
  if (first < 10) {
    putchar('0' + first);
    return;
  }
  print(first / 10);
  putchar(first % 10 + '0');
}
template <class T>
inline void println(T first) {
  print(first);
  putchar('\n');
}
template <class T>
inline void printsp(T first) {
  print(first);
  putchar(' ');
}
template <class T1, class T2>
inline void print(T1 x1, T2 x2) {
  printsp(x1), println(x2);
}
template <class T1, class T2, class T3>
inline void print(T1 x1, T2 x2, T3 x3) {
  printsp(x1), printsp(x2), println(x3);
}
template <class T1, class T2, class T3, class T4>
inline void print(T1 x1, T2 x2, T3 x3, T4 x4) {
  printsp(x1), printsp(x2), printsp(x3), println(x4);
}
template <class T1, class T2, class T3, class T4, class T5>
inline void print(T1 x1, T2 x2, T3 x3, T4 x4, T5 x5) {
  printsp(x1), printsp(x2), printsp(x3), printsp(x4), println(x5);
}
int power(int a, int b, int m, int ans = 1) {
  for (; b; b >>= 1, a = 1LL * a * a % m)
    if (b & 1) ans = 1LL * ans * a % m;
  return ans;
}
int a[300300], id[300300];
set<int> s;
bool cmp(int u, int v) {
  if (a[u] > a[v])
    return 1;
  else if (a[u] == a[v]) {
    if (u > v)
      return 1;
    else
      return 0;
  } else
    return 0;
}
double calc(int p) {
  s.insert(p);
  double A = 0;
  double B = 0;
  set<int>::iterator pre, nxt;
  pre = nxt = s.find(p);
  for (int i = 0; i < 50 and pre != s.begin(); i++) {
    pre--;
    A += (double)(*nxt - *pre) / (1ll << i);
    nxt--;
  }
  pre = nxt = s.find(p);
  nxt++;
  for (int i = 0; i < 50 and nxt != s.end(); i++) {
    B += (double)(*nxt - *pre) / (1ll << i);
    pre++;
    nxt++;
  }
  return A * B / 2;
}
int main() {
  int n;
  gn(n);
  for (int i = 0; i < n; i++) {
    gn(a[i]);
    id[i] = i;
  }
  sort(id, id + n, cmp);
  double ans = 0;
  s.insert(-1);
  s.insert(n);
  for (int i = 0; i < n; i++) {
    ans += calc(id[i]) * a[id[i]];
  }
  ans /= ((long long)n * n);
  printf("%.6lf\n", ans);
}
