#include <bits/stdc++.h>
using namespace std;
const int maxn = 200 + 2;
int n;
double ans;
double p[maxn];
int main() {
  scanf("%d", &n);
  for (int i = 0; i <= n; i++) scanf("%lf", &p[i]);
  for (int i = 0; i <= n; i++)
    if (n >= 2 * i)
      for (int j = 0; j <= n; j++)
        if (n <= 2 * j)
          ans = max(
              ans, (p[i] * (2 * j - n) + p[j] * (n - 2 * i)) / (2 * j - 2 * i));
  printf("%.10lf", ans);
  return 0;
}
