#include <bits/stdc++.h>
using namespace std;
int n;
double a[110], Ans;
int main() {
  std::ios::sync_with_stdio(false);
  cin >> n;
  for (int i = 0; i <= n; ++i) cin >> a[i];
  for (int i = 0; i <= (n + 1) / 2 - 1; ++i)
    for (int j = (n + 1) / 2; j <= n; ++j)
      Ans =
          max(Ans, (a[i] * (2 * j - n) + a[j] * (n - 2 * i)) / (2 * j - 2 * i));
  printf("%.10lf\n", Ans);
  return 0;
}
