#include <bits/stdc++.h>
int n, m, nn;
double p[1100], dis[1030];
struct XD {
  int x, y;
  double l;
} ed[94000];
bool Check(double avg) {
  int i, j;
  for (i = 0; i <= nn; i++) dis[i] = 0;
  for (i = 0; i <= nn + 2; i++)
    for (j = 0; j < m; j++)
      if (dis[ed[j].y] > dis[ed[j].x] + avg - ed[j].l)
        dis[ed[j].y] = dis[ed[j].x] + avg - ed[j].l;
  for (j = 0; j < m; j++)
    if (dis[ed[j].y] > dis[ed[j].x] + avg - ed[j].l + 1e-8) return 1;
  return 0;
}
int main() {
  int i, j;
  scanf("%d", &n);
  for (i = 0; i <= n; i++) scanf("%lf", &p[i]);
  nn = n * 3;
  for (i = 0; i <= nn; i++) {
    for (j = 0; j <= i && j <= n; j++) {
      int r = i - j + n - j;
      if (r < 0 || r > nn) continue;
      ed[m].x = i;
      ed[m].y = r;
      ed[m].l = p[j];
      m++;
    }
  }
  double l = 0, r = 1;
  for (int k = 0; k < 40; k++) {
    double mid = (l + r) / 2;
    if (Check(mid))
      l = mid;
    else
      r = mid;
  }
  printf("%.10lf\n", l);
  return 0;
}
