#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep1(i,n) for(int i=1;i<=(int)(n);i++)
#define fs first
#define sc second
typedef pair<ll, ll> l_l;
#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))

int main(){
   int n;
   cin>>n;
  vector<double>v(n+2);
  rep(i,n)cin>>v[i];
  sort(v.begin(),v.end());
  if(n==2)cout<<(v[0]+v[1])/2<<endl;
  else {
    double s;
  for(int i=0;i<n-2;i++){
    s=(((v[i]+v[i+1])/2)+v[i+2])/2;
  }
 
   cout<<s<<endl;
}
