#include <bits/stdc++.h>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl;
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
typedef long long ll;
// #define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep1(i,n) for(int i=1;i<=(int)(n);i++)
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(int)(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const long double pi = 3.1415926535897932384626433832795028841971L;
#define Sp(p) cout<<setprecision(25)<< fixed<<p<<endl;
// int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
// int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
vi dx = {1, 0, -1, 0}, dy = {0, 1, 0, -1};
// vi dx2 = { 1,1,0,-1,-1,-1,0,1 }, dy2 = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
const ll MOD = 1000000007;
// const ll MOD = 998244353;
// #define mp make_pair
//#define endl '\n'

int n;
const int N = 10;
vi a(N);
vector<vector<vector<double>>> memo(1 << N, vector<vector<double>>(N * 20 + 1, vector<double>(2, -1)));

double calc(int state, int score, int turn) {
    if (memo[state][score][turn] >= 0) return memo[state][score][turn];

    int sum = 0;
    rep (i, n) {
        if (state & (1 << i)) sum += a[i];
    }
    int you = sum - score;
    pair<double, int> ma(-inf, -1);
    rep (i, n) {
        if (state & (1 << i)) continue;
        if (a[i] == 1) {
            double ex = 1 - calc(state | (1 << i), you, 1 - turn);
            chmax(ma, {ex, i});
            continue;
        }
        double X = calc(state | (1 << i), you, 1 - turn);
        double mi = inf;
        rep (j, n) {
            if (state & (1 << j)) continue;
            double Y = calc(state | (1 << j), score, turn);
            if (a[j] == 1) {
                double f = 1. / a[i] * (1 - X) + (1 - 1. / a[i]) * (1 - (1 - Y));
                chmin(mi, f);
                continue;
            }
            double r = 1. / a[i];
            double f = r * (1 - X) + (1 - r) * (1 - 1. / a[j] * (1 - Y)) - (1 - r) * (1 - 1./a[j]);
            f /= (1 - (1. - r) * (1. - 1. / a[j]));
            chmin(mi, f);
        }
        chmax(ma, {mi, i});
    }
    // DEBUG(state);
    // DEBUG(score);
    // DEBUG(turn);
    // DEBUG(ma);

    memo[state][score][turn] = ma.first;
    return ma.first;
}

signed main() {
    fio();
    
    cin >> n;
    a.resize(n);
    int sum = 0;
    rep (i, n) {
        cin >> a[i];
        sum += a[i];
    }

    rep (i, sum + 1) {
        rep (j, 2) {
            int me = i, you = sum - i;
            if (me != you) {
                if (me > you) memo[(1 << n) - 1][i][j] = 1;
                else memo[(1 << n) - 1][i][j] = 0;
            }
            else {
                if (j == 0) memo[(1 << n) - 1][i][j] = 0;
                else memo[(1 << n) - 1][i][j] = 1;
            }
        }
    }

    Sp(calc(0, 0, 0));
}