#pragma GCC optimization ("O3")

#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using vec = vector<ll>;
using mat = vector<vec>;
using pll = pair<ll,ll>;

#define INF (1LL<<61)
#define MOD 1000000007LL 
//#define MOD 998244353LL
#define EPS (1e-10)

#define PR(x) cout << (x) << endl
#define PS(x) cout << (x) << " "
#define REP(i,m,n) for(ll (i)=(m),(i_len)=(n);(i)<(i_len);++(i))
#define FORE(i,v) for(auto (i):v)
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((ll)(x).size())
#define REV(x) reverse(ALL((x)))
#define ASC(x) sort(ALL((x)))
#define DESC(x) {ASC((x)); REV((x));}
#define BIT(s,i) (((s)>>(i))&1)
#define pb push_back
#define fi first
#define se second

template<class T> inline int chmin(T& a, T b) {if(a>b) {a=b; return 1;} return 0;}
template<class T> inline int chmax(T& a, T b) {if(a<b) {a=b; return 1;} return 0;}
class mint {
public:
    ll x;
    mint(ll x=0) : x((x%MOD+MOD)%MOD) {}
    mint operator-() const {return mint(-x);}
    mint& operator+=(const mint& a) {if((x+=a.x)>=MOD) x-=MOD; return *this;}
    mint& operator-=(const mint& a) {if((x+=MOD-a.x)>=MOD) x-=MOD; return *this;}
    mint& operator*=(const mint& a) {(x*=a.x)%=MOD; return *this;}
    mint operator+(const mint& a) const {mint b(*this); return b+=a;}
    mint operator-(const mint& a) const {mint b(*this); return b-=a;}
    mint operator*(const mint& a) const {mint b(*this); return b*=a;}
    mint pow(ll t) const {if(!t) return 1; mint a=pow(t>>1); return (t&1?*this*a:a)*a;}
    mint inv() const {return pow(MOD-2);}
    mint& operator/=(const mint& a) {return *this*=a.inv();}
    mint operator/(const mint& a) const {mint b(*this); return b/=a;}
};
istream &operator>>(istream& is, mint& a) {ll t; is>>t; a=t; return is;}
ostream &operator<<(ostream& os, const mint& a) {return os<<a.x;}
using mvec = vector<mint>;
using mmat = vector<mvec>;
using dvec = vector<double>;
using dmat = vector<dvec>;

ll N;
vec A;
map<vec,double> mp;

double solve(ll c, ll state, ll win)
{
    vec tmp = {c, state, win};
    if(mp.count(tmp)) return mp[tmp];
    if(state == 0) {
        ll s = 0, t = 0;
        REP(i,0,N) {
            if(BIT(win,i)) s += A[i];
            else t += A[i];
        }
        if((c == 0 && s > t) || (c == 1 && s <= t)) return mp[tmp] = 1;
        else return mp[tmp] = 0;
    }
    double res = 0;
    REP(a,0,N) {
        if(!BIT(state,a)) continue;
        if(A[a] == 1) {
            ll nw = win;
            if(c == 0) nw ^= 1LL<<a;
            chmax(res, 1-solve(c^1, state^(1LL<<a), nw));
            continue;
        }
        double score = 1;
        REP(b,0,N) {
            if(!BIT(state,b)) continue;
            double coef = (A[a]*A[b])/(double)(A[a]+A[b]-1);
            double val = 0;
            if(c == 0) {
                val += coef*(1-solve(c^1, state^(1LL<<a), win^(1LL<<a)))/A[a];
                val += coef*solve(c, state^(1LL<<b), win)*(A[a]-1)/A[a]/A[b];
            }
            else {
                val += coef*(1-solve(c^1, state^(1LL<<a), win))/A[a];
                val += coef*solve(c, state^(1LL<<b), win^(1LL<<b))*(A[a]-1)/A[a]/A[b];
            }
            chmin(score, val);
        }
        chmax(res, score);
    }
    return mp[tmp] = res;
}

int main()
{
    cin >> N;
    A = vec(N);
    REP(i,0,N) cin >> A[i];

    double ans = solve(0, (1LL<<N)-1, 0);
    cout << setprecision(12) << ans << endl;

    return 0;  
}
/*



*/