#include <bits/stdc++.h>
 
 
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
using namespace __gnu_pbds;
 
 
using namespace std;
 
#if DEBUG && !ONLINE_JUDGE
    #include "debug.h"
#else
    #define debug(...)
#endif
 
typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> ii;
typedef vector<vector<int> > vvi;
typedef vector<vector<ii> > vvii;
 
#define pb push_back
#define mp make_pair
#define all(x) x.begin(),x.end()
#define sz(x) (int)x.size()
#define fill(a,x) memset(a,x,sizeof(a))
#define ff first
#define ss second
#define trav(a, x) for(auto& a : x) 
#define FOR(i,a,b) for(int i = a; i<=b; ++i)
#define NFOR(i,a,b) for(int i = a; i>=b; --i)
const ll INF = 1e18;
const int mod = 1e9+9;
ll gcd(ll a,ll b){if (a==0) return b;return gcd(b%a,a);}
ll lcm(ll a,ll b){return a*(b/gcd(a,b));}
ll Abs(ll a){if(a>0)return a;return -a;}
ll Ceil(ll a,ll b){if(a%b==0)return a/b;else return a/b+1;}
double Abs(double a){if(a>0)return a;return -a;}
 
//*X.find_by_order(2) element at index=2
//X.order_of_key(1) how many elements strictly less than 1
 
#define ordered_set tree<int, null_type,less_equal<int>, rb_tree_tag,tree_order_statistics_node_update> 
 
inline int pow_(ll x, ll y,ll p){
  int r = 1; while(y){if(y & 1) r = r * x % p; y >>= 1; x = x * x % p;} return r;
}
inline int inv_(int x){return pow_(x, mod - 2, mod);}
inline int add(int a, int b){a += b; if(a >= mod) a -= mod; return a;}
inline int mul(int a, int b){return a * 1LL * b % mod;}
inline int sub(int a, int b){a -= b; if(a < 0) a += mod; return a;}

int main(){

	#ifdef LOCAL_TEST
    freopen("in.txt","r",stdin);
    //freopen("out.txt", "w", stdout);
    #else
    ios_base::sync_with_stdio(false);cin.tie(NULL);
    #endif
    ll n;
    cin>>n;
    double a[n+5] = {0};
    for(int i=1;i<=n;i++)cin>>a[i];

    double dp[n+5][n+5] = {0};

    for(int l=1;l<=n;l++){
    	for(int i=1;i<=n-l+1;i++){
    		int j = i+l-1;
    		if(i == j){
    			dp[i][j] = a[i];
    		} else {
    			for(int k=i;k<j;k++){
    				dp[i][j] = max(dp[i][j],(dp[i][k]+dp[k+1][j])/2);
    			}
    		}
    	}
    }
    printf("%0.10f\n",dp[1][n]);
}