#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);   }