#include <bits/stdc++.h>
using namespace std;
int n;
double p[102], max1;
int main() {
  cin >> n;
  for (int i = 0; i <= n; i++) cin >> p[i];
  for (int i = 0; i <= (n + 1) / 2 - 1; i++)
    for (int j = (n + 1) / 2; j <= n; j++)
      max1 = max(max1,
                 (p[i] * (2 * j - n) + p[j] * (n - 2 * i)) / (2 * j - 2 * i));
  printf("%.10llf", max1);
  return 0;
}
