#include <bits/stdc++.h>
using namespace std;
const int maxn = 105;
double p[maxn], ret;
int n;
void init() {
  scanf("%d", &n);
  for (int i = 0; i <= n; i++) scanf("%lf", &p[i]);
}
void work() {
  ret = 0;
  for (int i = 0; i + i <= n; i++)
    for (int j = n / 2 + 1; j <= n; j++) {
      double tmp = (p[i] * (j * 2 - n) + p[j] * (n - i * 2)) / ((j - i) * 2);
      if (tmp > ret) ret = tmp;
    }
}
void print() { printf("%.10lf\n", ret); }
int main() {
  init();
  work();
  print();
  return 0;
}
