#include <bits/stdc++.h>
using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
//typedef vector<vector<ll>> Graph;

const ll mod = 1e9 + 7;
//const ll mod = 998244353;

#define REP(i,n) for(ll i=0;i<(ll)n;i++)
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define spa << " " <<
#define fi first
#define se second

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; }

template<class S, class T> ostream& operator << (ostream& os, const pair<S, T> v){
os << "(" << v.first << ", " << v.second << ")"; return os;
}
template<class T> ostream& operator << (ostream& os, const vector<T> v){
for(int i = 0; i < (int)v.size(); i++){if(i > 0){os << " ";} os << v[i];} return os;
}
template<class T> ostream& operator << (ostream& os, const vector<vector<T>> v){
for(int i = 0; i < (int)v.size(); i++){if(i > 0){os << endl;} os << v[i];} return os;
}

template<typename T> void debug(vector<vector<T>>&v,ll h,ll w){for(ll i=0;i<h;i++)
{cerr<<v[i][0];for(ll j=1;j<w;j++)cerr spa v[i][j];cerr<<endl;}};
template<typename T> void debug(vector<T>&v,ll n){if(n!=0)cerr<<v[0];
for(ll i=1;i<n;i++)cerr spa v[i];
cerr<<endl;};

string num2bit(ll num, ll len){
    string bit = "";
    REP(i, len){
    bit += char('0'+(num>>i & 1));
    }
    reverse(bit.begin(), bit.end());
    return bit;
}

ll N;
vector<ll> A(15, 0);
pdd dp[600][1050];

pdd rec(ll D, ll mask){
    if(dp[D][mask].first >= 0.0) return dp[D][mask]; 
    if(mask==0){
        if(D>300) return {1.0, 1.0};
        else return {0.0, 0.0};
    }

    double p = 0.0;
    double q = 0.0;

    double p_max = 0.0;
    REP(i, N){
        if(mask>>i & 1){
            double q_plus = rec(D+A[i], mask^(1ll<<i)).second;
            double q_min = 1.0;
            REP(j, N){
                if(mask>>j & 1){    
                    double p_minus = rec(D-A[j], mask^(1ll<<j)).first;
                    double r = 1.0/A[i] + 1.0/A[j] - 1.0/(A[i] * A[j]);
                    double q_tmp = (1.0/A[j] * p_minus + (A[j]-1.0)/(A[i]*A[j]) * q_plus)/r;
                    chmin(q_min, q_tmp);
                }
            }
            double p_tmp = 1.0/A[i] * q_plus + (1.0 - 1.0/A[i]) * q_min;
            if(chmax(p_max, p_tmp)){
                p = p_max;
                q = q_min;
            }
        }
    }
    
    pdd res = {p, q};
    dp[D][mask] = res;
    return res;
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> N;
    REP(i, N) cin >> A[i];

    REP(i, 600)REP(j, 1050) dp[i][j] = {-1, -1};

    auto res = rec(300, (1ll<<N)-1);
    printf("%.10f\n", res.first);

    return 0;
}