#include <bits/stdc++.h>
using namespace std;
int a[69];
double ans;
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  for (int i = 1; i < n - 1; i++) {
    ans = (a[i] + a[i - 1]) / 2;
  }
  cout << ans;
}
