#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  scanf("%d", &N);
  static double P[101];
  for (int i = 0; i <= N; i++) cin >> P[i];
  double Ans = 0;
  for (int i = 0; i <= N / 2; i++)
    for (int j = (N + 1) / 2; j <= N; j++) {
      int W0 = j * 2 - N, W1 = N - i * 2;
      if (!W0 && !W1) W0 = W1 = 1;
      Ans = max(Ans, (P[i] * W0 + P[j] * W1) / (W0 + W1));
    }
  printf("%0.10lf\n", Ans);
  return 0;
}
