#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; i++)
#define rep2(i, x, n) for(int i = x; i <= n; i++)
#define rep3(i, x, n) for(int i = x; i >= n; i--)
#define elif else if
#define sp(x) fixed << setprecision(x)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define sz(x) (int)x.size()
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;
const ll MOD = 1e9+7;
//const ll MOD = 998244353;
const int inf = (1<<30)-1;
const ll INF = (1LL<<60)-1;
const ld EPS = 1e-10;
template<typename T> bool chmax(T &x, const T &y) {return (x < y)? (x = y, true) : false;};
template<typename T> bool chmin(T &x, const T &y) {return (x > y)? (x = y, true) : false;};

int main(){
    int N;
    cin >> N;
    int A[N];
    rep(i, N) cin >> A[i];
    int sum[1<<N];
    rep(i, 1<<N){
        sum[i] = 0;
        rep(j, N) if(i&(1<<j)) sum[i] += A[j];
    }
    int all = sum[(1<<N)-1];
    ld dp[1<<N][201][2];
    rep(i, 1<<N) rep(j, 201) rep(k, 2) dp[i][j][k] = 0.0;
    rep(j, 201){
        if(j*2 > all) rep(k, 2) dp[0][j][k] = 1.0;
    }
    rep(i, 1<<N){
        if(i == 0) continue;
        rep(j, 201){
            ld memo1[N][N], memo2[N][N];
            fill(memo1[0], memo1[N], -1.0), fill(memo2[0], memo2[N], -1.0);
            rep(k, N) rep(l, N){
                if(!(i&(1<<k)) || !(i&(1<<l))) continue;
                if(j+A[k] > 200) continue;
                ld s = ld(1)/ld(A[k]), t = ld(1)/ld(A[l]);
                ld p = dp[i^(1<<k)][j+A[k]][1], q = dp[i^(1<<l)][j][0];
                ld x = (s*p+(1-s)*t*q)/(s+t-s*t);
                ld y = t*q+(1-t)*x;
                memo1[k][l] = x, memo2[k][l] = y;
            }
            int res[N];
            rep(k, N){
                res[k] = -1;
                rep(l, N){
                    if(memo1[k][l] < -EPS) continue;
                    if(res[k] == -1) res[k] = l;
                    if(memo1[k][l] < memo1[k][res[k]]) res[k] = l;
                }
            }
            int a = 0;
            rep(k, N) if(memo1[k][res[k]] > memo1[a][res[a]]) a = k;
            dp[i][j][0] = memo1[a][res[a]], dp[i][j][1] = memo2[a][res[a]];
        }
    }
    cout << sp(10) << dp[(1<<N)-1][0][0] << endl;
}