#include <bits/stdc++.h>
using namespace std;
const int N = 110;
double p[N], Ans = 0;
int main() {
  int n;
  cin >> n;
  for (int i = 0; i <= n; i++) cin >> p[i];
  for (int i = 0; i * 2 < n; i++)
    for (int j = n; j * 2 > n; j--)
      Ans = max(Ans, (p[i] / abs(n - 2 * i) + p[j] / abs(n - 2 * j)) /
                         (1.0 / abs(n - 2 * i) + 1.0 / abs(n - 2 * j)));
  if (n % 2 == 0) Ans = max(Ans, p[n / 2]);
  printf("%.10f\n", Ans);
  return 0;
}
