#include <bits/stdc++.h>
using namespace std;
int main(void) {
  long long N;
  cin >> N;
  vector<double> V;
  V.resize(N);
  for (int i = 0; i < (int)(N); i++) cin >> V[i];
  while (1) {
    if (V.size() == 1) break;
    auto itr = min_element(V.begin(), V.end());
    auto itr2 = V.begin();
    if (itr == V.begin())
      itr2 = V.begin() + 1;
    else if (itr == V.end() - 1)
      itr2 = V.end() - 2;
    else if (*(itr - 1) > *(itr + 1))
      itr2 = itr + 1;
    else
      itr2 = itr - 1;
    *itr = (*itr) / 2. + (*itr2) / 2.;
    V.erase(itr2);
  }
  printf("%.8f\n", V[0]);
  return 0;
}
