#include <bits/stdc++.h>
using namespace std;
int n;
double p[200];
int main() {
  scanf("%d", &n);
  for (int i = 0; i <= n; ++i) scanf("%lf", &p[i]);
  double E, ans = p[n / 2];
  for (int i = n / 2 + 1; i <= n; ++i)
    for (int j = 0; j <= (n - 1) / 2; ++j) {
      E = 0.5 * (p[j] * (i + i - n) + p[i] * (n - j - j)) / (i - j);
      if (ans < E) ans = E;
    }
  printf("%.10lf\n", ans);
  return 0;
}
