#include <bits/stdc++.h>
using namespace std;

int main(){
  int a,i,j,tmp;
  double b;
  b=0;
  
  cin >> a;
  
  vector<double> vec(a);
  for(i=0;i<a;i++){
    cin >> vec[i];
  }
  
  vector<double> vek;
  
  for(i=0;i<a;i--){
    vec[i]=min(vec(a));
    vec.pop_back(vec[i]);
    vek.push_back(vec[i]);
  }
  
  
  
  for(i=0;i<a-1;i++){
    vek[i+1]=(vek[i]+vek[i+1])/2;
  }
  
  b=(vek[a-2]+vek[a-1])/2;
  
  cout << b;
}
