#include <bits/stdc++.h>
using namespace std;
const int maxn = 300;
const long double inf = 2e9;
long double dist[maxn][maxn], p[maxn];
int n;
bool check(long double x) {
  for (int i = 0; i <= 2 * n; i++) {
    fill(dist[i], dist[i] + 2 * n + 1, inf);
    dist[i][i] = 0;
  }
  for (int i = 0; i <= 2 * n; i++) {
    for (int j = 0; j <= n; j++) {
      if (i + n - 2 * j >= 0 && i + n - 2 * j <= 2 * n) {
        dist[i][i + n - 2 * j] = min(dist[i][i + n - 2 * j], 1 - p[j] - x);
      }
    }
  }
  for (int k = 0; k <= 2 * n; k++) {
    for (int i = 0; i <= 2 * n; i++) {
      for (int j = 0; j <= 2 * n; j++) {
        dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
      }
    }
  }
  for (int i = 0; i <= 2 * n; i++) {
    if (dist[i][i] < 0) return 1;
  }
  return 0;
}
long double bs() {
  long double l = 0, r = 1;
  for (int i = 0; i <= 21; i++) {
    long double m = (l + r) / 2;
    if (check(m)) {
      r = m;
    } else {
      l = m;
    }
  }
  return l;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n;
  for (int i = 0; i <= n; i++) {
    cin >> p[i];
  }
  cout << setprecision(20) << 1 - bs();
}
