#include <bits/stdc++.h>
using namespace std;
int n;
double p[110], ans;
int main() {
  scanf("%d", &n);
  for (int i = 0; i <= n; ++i) scanf("%lf", &p[i]);
  for (int i = 0; i <= n / 2; ++i)
    for (int j = n / 2 + 1; j <= n; ++j)
      ans = max(ans, ((n - 2 * i) * p[j] - (n - 2 * j) * p[i]) / (2 * (j - i)));
  printf("%.10lf", ans);
}
