#include <bits/stdc++.h>

using namespace std;

int main(){
  int N;
  cin >> N;
  
  double v[N]
  for(int i=0;i<M;i++){
    cin >> v[i];
  }
  
  sort(v,v+N);

  double tmp = (v[0] + v[1])/2.0;
  double sum = 0.0;
  for(int i=3;i<N;i++){
    sum = (tmp + v[i])/2.0;
  }

  cout << sum << endl;
  return 0;

}

