#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
typedef long long ll;
#define _GLIBCXX_DEBUG
typedef vector<int> vec;
typedef vector<ll> lvec;
typedef vector<char>cvec;
typedef pair<ll, ll> LP;
typedef tuple<ll, ll, ll> LT;
typedef pair<int, int> P;
typedef tuple<int, int, int> T;
int main()	{
  int n;
  cin>>n;
  vector<int>v(n);
  vector<double>d(n);
  rep(i,n) cin>>v[i];
  rep(i,n-1){
    sort(v.begin(),v.end());
    d[i]=(v[0]+v[1])/=2;
  }
  cout<<fixed<<setprecision(5)<<d[n-2]<<endl;
}