#include <bits/stdc++.h>
using namespace std;
bool cmp(pair<long long, long long> a, pair<long long, long long> b) {
  return a.second < b.second;
}
long long mod = 1e9 + 7;
signed main() {
  vector<long long> ret;
  long long n;
  cin >> n;
  vector<double> v(n);
  for (long long i = 0; i < n; i++) cin >> v[i];
  double ans = (v[0] + v[1]) / 2;
  if (n > 2) {
    for (int i = 2; i < n; i++) {
      ans = (ans + v[i]) / 2;
    }
  }
  cout << fixed << setprecision(10) << ans << endl;
}
