#include <bits/stdc++.h>   #pragma GCC optimize( Ofast )   #pragma GCC optimize( unroll-loops )   #pragma GCC target( sse,sse2,sse3,ssse3,abm,mmx,tune=native )   using namespace std;   long long gcd(long long i, long long j) {     if (j == 0)       return i;     else       return gcd(j, i % j);   }   template <typename T>   inline T getint() {     T val = 0;     char c;     bool neg = false;     while ((c = getchar()) && !(c >=  0  && c <=  9 )) {       neg |= c ==  - ;     }     do {       val = (val * 10) + c -  0 ;     } while ((c = getchar()) && (c >=  0  && c <=  9 ));     return val * (neg ? -1 : 1);   }   const long long INF = 1e9 + 100;   const int mod = 1000000007;   const long double eps = 1e-10, pi = acosl(-1);   const long long maxN = 300010, maxT = 10010, A = 179, mid = 150;   mt19937 mt_rand(time(0));   long long bp(long long et, long long b) {     b %= mod - 1;     long long res = 1;     for (int i = 30; i >= 0; --i) {       res = (res * res) % mod;       if ((b & (1 << i)) != 0) res = (res * et) % mod;     }     return res;   }   void panic() {     cout <<  -1 n ;     exit(0);   }   const int byben_size = 23;   vector<int> merge(const vector<int>& a, const vector<int>& b,                     bool want_mx = true) {     int s1 = a.size(), s2 = b.size();     int sz = min(s1 + s2, byben_size);     vector<int> r(sz);     if (!want_mx) {       int y1 = 0, y2 = 0;       int y = 0;       while (y < sz && y1 < s1 && y2 < s2) {         if (a[y1] < b[y2])           r[y++] = a[y1++];         else           r[y++] = b[y2++];       }       while (y < sz && y1 < s1) r[y++] = a[y1++];       while (y < sz && y2 < s2) r[y++] = b[y2++];     } else {       int y1 = s1 - 1, y2 = s2 - 1;       int y = sz - 1;       while (y >= 0 && y1 >= 0 && y2 >= 0) {         if (a[y1] > b[y2])           r[y--] = a[y1--];         else           r[y--] = b[y2--];       }       while (y >= 0 && y1 >= 0) r[y--] = a[y1--];       while (y >= 0 && y2 >= 0) r[y--] = b[y2--];     }     return r;   }   vector<int> t[1 << 18];   int sz = 1 << 17;   int a[maxN];   vector<int> l1[maxN], r1[maxN];   inline void add(int l, int r, int id, bool want_mx) {     for (l += sz, r += sz; l <= r; l >>= 1, r >>= 1) {       if (l & 1) {         int v = l++;         t[v].push_back(id);         int szz = t[v].size();         int rr = szz;         --szz;         while (szz > 0 && t[v][szz] < t[v][szz - 1]) {           swap(t[v][szz], t[v][szz - 1]);           --szz;         }         if (rr > byben_size) {           if (want_mx)             t[v].erase(t[v].begin());           else             t[v].pop_back();         }       }       if (~r & 1) {         int v = r--;         t[v].push_back(id);         int szz = t[v].size();         int rr = szz;         --szz;         while (szz > 0 && t[v][szz] < t[v][szz - 1]) {           swap(t[v][szz], t[v][szz - 1]);           --szz;         }         if (rr > byben_size) {           if (want_mx)             t[v].erase(t[v].begin());           else             t[v].pop_back();         }       }     }   }   vector<int> get(int v, bool want_mx) {     vector<int> r;     v |= sz;     for (v = v | sz; v; v >>= 1) {       r = merge(t[v], r, want_mx);     }     return r;   }   long double pw[maxT];   void solve() {     pw[0] = 1;     for (int i = 1; i < maxT; ++i) pw[i] = pw[i - 1] * 2;     int n = getint<int>();     for (int i = 1; i <= n; ++i) {       a[i] = getint<int>();     }     add(0, sz - 1, 0, 1);     for (int i = 1; i <= n; ++i) {       add(0, a[i], i, 1);       l1[i] = get(a[i], 1);     }     for (int i = 0; i < 2 * sz; ++i) t[i].clear();     add(0, sz - 1, n + 1, 0);     for (int i = n; i > 0; --i) {       add(0, a[i], i, 0);       r1[i] = merge({i}, get(a[i] + 1, 0), 0);     }     long double ans = 0;     for (int i = 1; i <= n; ++i) {       for (int j = 1; j < l1[i].size(); ++j) {         for (int k = 0; k + 1 < r1[i].size(); ++k) {           long long cnt =               (long long)(l1[i][j] - l1[i][j - 1]) * (r1[i][k + 1] - r1[i][k]);           int pww = k + l1[i].size() - j;           if (pww > byben_size) break;           ans += (long double)cnt / pw[pww] * a[i];         }       }     }     cout << fixed << ans / n / n <<   n ;   }   int32_t main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     cout.precision(20);     int t = 1;     while (t--) {       solve();     }     return 0;   }