#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007;
// const int MOD = 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
const int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n; cin >> n;
  vector<int> a(n); REP(i, n) cin >> a[i];
  vector dp(2, vector(1 << n, vector(1 << n, -1.0)));
  function<double(int, int, int)> rec = [&](int turn, int nu, int ki) {
    double &d = dp[turn][nu][ki];
    if (d >= 0) return d;
    int removed = nu | ki;
    if (removed == (1 << n) - 1) {
      int sum = 0;
      REP(i, n) sum += a[i] * (nu >> i & 1 ? 1 : -1);
      return d = sum > 0 ? 1 : 0;
    }
    if (turn == 0) {  // null
      d = 0;
      REP(i, n) {
        if (removed >> i & 1) continue;
        double mn = 1;
        REP(j, n) {
          if (removed >> j & 1) continue;
          double p = 0;
          p += rec(turn ^ 1, nu | (1 << i), ki) / a[i];
          p += (1 - 1. / a[i]) * rec(turn, nu, ki | (1 << j)) / a[j];
          if (a[i] > 1 && a[j] > 1) p /= 1 - (1 - 1. / a[i]) * (1 - 1. / a[j]);
          chmin(mn, p);
        }
        chmax(d, mn);
      }
    } else {  // kiri
      d = 1;
      REP(i, n) {
        if (removed >> i & 1) continue;
        double mx = 0;
        REP(j, n) {
          if (removed >> j & 1) continue;
          double p = 0;
          p += rec(turn ^ 1, nu, ki | (1 << i)) / a[i];
          p += (1 - 1. / a[i]) * rec(turn, nu | (1 << j), ki) / a[j];
          if (a[i] > 1 && a[j] > 1) p /= 1 - (1 - 1. / a[i]) * (1 - 1. / a[j]);
          chmax(mx, p);
        }
        chmin(d, mx);
      }
    }
    return d;
  };
  cout << rec(0, 0, 0) << '\n';
  return 0;
}