#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<double> a(n);
  double ans = 0, x = 0;
  for (int i = 0; i < (n); ++i) cin >> a[i];
  for (int i = 0; i < (n); ++i) {
    for (int j = i + 1; j < n; j++) {
      x = (a[i] + a[j]) / 2;
      ans = max(ans, x);
    }
  }
  cout << ans << endl;
  return 0;
}
