#include <bits/stdc++.h>
using namespace std;
void Get(int &T) {
  char C;
  bool F = 0;
  for (; C = getchar(), C < '0' || C > '9';)
    if (C == '-') F = 1;
  for (T = C - '0'; C = getchar(), C >= '0' && C <= '9'; T = T * 10 + C - '0')
    ;
  F && (T = -T);
}
double W[105];
int N;
void Init() {
  Get(N);
  for (int i = 0; i <= N; i++) scanf("%lf", W + i);
}
double Ans;
void Work() {
  for (int i = 0; i <= N + 1; i++)
    for (int j = i + 1; j <= N + 1; j++) {
      if (i <= N && j <= N) {
        double Xi = (N * .5 - j) / (double(i - j));
        double Xj = 1 - Xi;
        if (Xi > -1e-12 && Xj > -1e-12) {
          if (Ans < Xi * W[i] + Xj * W[j]) Ans = Xi * W[i] + Xj * W[j];
        }
      } else {
        double Xi = 1;
        double Xj = (N * .5 - i * Xi);
        if (Xi > -1e-12 && Xj > -1e-12) {
          if (Ans < Xi * W[i] + Xj * W[j]) Ans = Xi * W[i] + Xj * W[j];
        }
      }
    }
}
void Output() { printf("%.12lf\n", Ans); }
int main() {
  Init();
  Work();
  Output();
  return 0;
}
