#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define M 1000000007
#define N 1000016
#define ff first.first
#define fs first.second
#define sf second.first
#define ss second.second
#define f first
#define s second
#define inf 9000000000000000000

int main()
{
    // ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
   vector<double> v;
   ll n;
   cin>>n;
   for(ll i=0; i<n; i++) {
        cin>>x;
        v.push_back(x);
   }
   
   double ans = (v[i]+v[i+1])/2;
   for(ll i=2; i<n; i++) {
        ans = (ans + v[i])/2l 
   }
   
   cout<<fixed<<setprecision(10)<<ans<<"\n";

    return 0;
}
