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

void chmax(double& a, double b){
    a = max(a, b);
}
void chmin(double& a, double b){
    a = min(a, b);
}

int nth_bit(int64_t num, int n){
    return (num >> n) & 1;
}

int main(){
    int N;
    cin >> N;
    vector<double> A(N);
    for(int i=0; i<N; i++) cin >> A[i];

    int B = 1<<N;
    static double dp[1024][1024][2];
    for(int s0=0; s0<B; s0++){
        int sum0 = 0, sum1 = 0;
        for(int i=0; i<N; i++) (nth_bit(s0, i) ? sum0 : sum1) += A[i];
        for(int k=0; k<2; k++) dp[s0][B-1-s0][k] = (sum0 > sum1);
    }

    for(int s0=B-1; s0>=0; s0--) for(int s1=B-1; s1>=0; s1--) if((s0&s1) == 0 && (s0|s1) != B-1){
        vector<int> yet;
        for(int i=0; i<N; i++) if(nth_bit(s0|s1, i) == 0) yet.push_back(i);
        
        dp[s0][s1][0] = 0;
        for(int i : yet){
            double tmp = 1;
            for(int j : yet){
                double res = (A[j]*dp[s0|(1<<i)][s1][1] + (A[i]-1)*dp[s0][s1|(1<<j)][0]) / (A[i]+A[j]-1);
                chmin(tmp, res);
            }
            chmax(dp[s0][s1][0], tmp);
        }

        dp[s0][s1][1] = 1;
        for(int j : yet){
            double tmp = 0;
            for(int i : yet){
                double res = ((A[j]-1)*dp[s0|(1<<i)][s1][1] + A[i]*dp[s0][s1|(1<<j)][0]) / (A[i]+A[j]-1);
                chmax(tmp, res);
            }
            chmin(dp[s0][s1][1], tmp);
        }
    }
    cout << fixed << setprecision(10) << dp[0][0][0] << endl;
    return 0;
}