#include <bits/stdc++.h>
double p[300];
int main() {
  int n, i, j, a, b;
  double ans;
  scanf("%d", &n);
  for (i = 0; i <= n; i++) scanf("%lf", &p[i]);
  if (n % 2 == 0)
    ans = p[n / 2];
  else
    ans = 0;
  for (i = 0; i < n - i; i++)
    for (j = n; j > n - j; j--) {
      a = n - i - i;
      b = j + j - n;
      if (ans < p[i] * b / (a + b) + p[j] * a / (a + b))
        ans = p[i] * b / (a + b) + p[j] * a / (a + b);
    }
  printf("%.10f\n", ans);
  return 0;
}
