#include <bits/stdc++.h>
#pragma warning(disable : 6031)
#pragma warning(disable : 4101)
using namespace std;
const int INF = 1e9;
const long long LINF = 1e18;
const double PI = acos(-1);
const int MAXN = 55;
int n, A[MAXN];
double ans;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d", &A[i]);
  }
  sort(A, A + n);
  ans += (A[0] + A[1]) / double(1 << (n - 1));
  for (int i = 2; i < n; i++) {
    ans += A[i] / 2.0;
  }
  printf("%lf\n", ans);
  return 0;
}
