#include <bits/stdc++.h>
using namespace std;
const int Inf = 1e9;
const double eps = 1e-7;
inline int read() {
  int s = 0, m = 0;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') m = 1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9')
    s = (s << 3) + (s << 1) + (ch ^ 48), ch = getchar();
  return m ? -s : s;
}
int n;
int Get[150];
double P[150], Ans, ret;
int main() {
  n = read();
  for (register int i = 0; i <= n; ++i) scanf("%lf", &P[i]);
  for (register int i = n / 2 + 1; i <= n; ++i)
    for (register int j = 0; j <= n / 2; ++j) {
      double x = (i << 1) - n, y = n - (j << 1);
      ret = (y * P[i] + x * P[j]) / (x + y);
      Ans = max(Ans, ret);
    }
  printf("%.10lf\n", Ans);
  return 0;
}
