#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
#include<complex>
#include<numeric>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
constexpr ll mod = 1000000007;
const ll INF = mod * mod;
typedef pair<int, int>P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
#define all(v) (v).begin(),(v).end()
typedef pair<ll, ll> LP;
typedef long double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-12;
const ld pi = acos(-1.0);

ll mod_pow(ll x, ll n, ll m) {
	ll res = 1;
	while (n) {
		if (n & 1)res = res * x % m;
		x = x * x % m; n >>= 1;
	}
	return res;
}
struct modint {
	ll n;
	modint() :n(0) { ; }
	modint(ll m) :n(m) {
		if (n >= mod)n %= mod;
		else if (n < 0)n = (n % mod + mod) % mod;
	}
	operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint& a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= mod; return a; }
modint operator-=(modint& a, modint b) { a.n -= b.n; if (a.n < 0)a.n += mod; return a; }
modint operator*=(modint& a, modint b) { a.n = ((ll)a.n * b.n) % mod; return a; }
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, ll n) {
	if (n == 0)return modint(1);
	modint res = (a * a) ^ (n / 2);
	if (n % 2)res = res * a;
	return res;
}

ll inv(ll a, ll p) {
	return (a == 1 ? 1 : (1 - p * inv(p % a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }

const int max_n = 1 << 17;
modint fact[max_n], factinv[max_n];
void init_f() {
	fact[0] = modint(1);
	for (int i = 0; i < max_n - 1; i++) {
		fact[i + 1] = fact[i] * modint(i + 1);
	}
	factinv[max_n - 1] = modint(1) / fact[max_n - 1];
	for (int i = max_n - 2; i >= 0; i--) {
		factinv[i] = factinv[i + 1] * modint(i + 1);
	}
}
modint comb(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[b] * factinv[a - b];
}


int n;
vector<int> a;

bool used[1 << 10][401][2];
ld memo[1 << 10][401][2];
ld calc(int s, int dif, int id) {
	if (s == 0) {
		if (dif > 200)return 1;
		else if (dif < 200)return 0;
		else {
			if (id == 1)return 1;
			else return 0;
		}
	}
	if (used[s][dif][id])return memo[s][dif][id];
	used[s][dif][id] = true;
	ld res = 0;
	rep(i, n) {
		if (s & (1 << i)) {

			ld mi = INF;
			rep(j, n)if (s & (1 << j)) {
				ld p = 1 / (ld)(a[i] - (a[i] - 1) * (a[j] - 1) / (ld)a[j]);
				ld ex = p * (1 - calc(s ^ (1 << i), 400 - (dif + a[i]), id ^ 1));
				ex += (1 - p) * calc(s ^ (1 << j), dif - a[j], id);
				mi = min(mi, ex);
			}
			res = max(res, mi);
		}
	}
	return memo[s][dif][id] = res;

}


ld dp[1 << 10][401][2];
void solve() {
	cin >> n; a.resize(n);
	rep(i, n)cin >> a[i];
	ld ans = calc((1 << n) - 1, 200, 0);
	cout << ans << "\n";
	/*rep(i, 401)rep(j, 2) {
		if (i > 200)dp[0][i][j] = 1;
		else if (i < 200)dp[0][i][j] = 0;
		else {
			if (j == 0)dp[0][i][j] = 0;
			else dp[0][i][j] = 1;
		}
	}
	rep1(i, (1 << n) - 1)rep(j, 401) {
		int tmp = 0;
		rep(j, n)if (i & (1 << j))tmp++;
		if (j < tmp * 20)continue;
		if (j > 400 - tmp * 20)continue;
		//0
		ld ma = -1; int chk1 = 0;
		rep(k, n) {
			if(i& (1 << k)) {
				ld p= 1 / (ld)(a[i] - (a[i] - 1) * (a[i] - 1) / (ld)a[i]);
				ld ex = p * (1 - dp[i ^ (1 << k)][400 - (j + a[i])][1]);
				ex += (1 - p) * dp[i ^ (1 << k)][j - a[i]][0];
				if (ex > ma) {
					ma = ex; chk1 = k;
				}
			}
		}
		ma = -1;int chk2 = 0;
		rep(k, n) {
			if (i & (1 << k)) {
				ld p = 1 / (ld)(a[i] - (a[i] - 1) * (a[i] - 1) / (ld)a[i]);
				ld ex = p * (1 - dp[i ^ (1 << k)][400 - (400-j + a[i])][0]);
				ex += (1 - p) * dp[i ^ (1 << k)][400-j - a[i]][1];
				if (ex > ma) {
					ma = ex; chk1 = k;
				}
			}
		}
		ld b = a[chk1], c = a[chk2];
		ld p = 1 / (b - (b - 1) * (c - 1) /c);
		dp[i][j][0]=p*(1-dp[i^(1<<k)][])
	}*/

	//ld ans = dp[(1 << n) - 1][200][0];
	//cout << ans << "\n";
}




signed main() {
	//ios::sync_with_stdio(false);
	//cin.tie(0);
	cout << fixed << setprecision(10);
	//init_f();
	//expr();
	//int t; cin >> t; rep(i, t)
	solve();
	return 0;
}