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