#include <bits/stdc++.h>
double p[111];
double ans[111][222][222];
int main() {
  int n, i, j, k, l;
  double res = -1e6;
  scanf("%d", &n);
  for (i = 0; i <= n; i++) scanf("%lf", p + i);
  for (i = 0; i <= n; i++)
    for (j = 0; j <= 2 * n; j++)
      for (k = 0; k <= 2 * n; k++) ans[i][j][k] = -1e6;
  for (i = 0; i <= n; i++) ans[i][i][0] = 0;
  for (k = 1; k <= 2 * n; k++)
    for (i = 0; i <= n; i++)
      for (j = 0; j <= 2 * n; j++)
        if (ans[i][j][k - 1] >= 0)
          for (l = 0; l <= n && l <= j; l++)
            if (j - l + n - l <= 2 * n &&
                ans[i][j][k - 1] + p[l] > ans[i][j - l + n - l][k]) {
              ans[i][j - l + n - l][k] = ans[i][j][k - 1] + p[l];
              if (i == j - l + n - l && ans[i][j - l + n - l][k] / k > res)
                res = ans[i][j - l + n - l][k] / k;
            }
  printf("%.10lf\n", res);
  return 0;
}
