#include <bits/stdc++.h>
const int N = 110;
double p[N];
int main() {
  int n, i, j;
  double ans = 0.0, temp;
  scanf("%d", &n);
  for (i = 0; i <= n; i++) scanf("%lf", &p[i]);
  for (i = 0; i <= n / 2; i++)
    for (j = n / 2 + 1; j <= n; j++) {
      temp = (p[i] * (j * 2 - n) + p[j] * (n - i * 2)) / 2 / (j - i);
      if (temp > ans) ans = temp;
    }
  printf("%.10lf", ans);
  return (0);
}
