#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
double dp[2][1<<10][1<<10];
int n;
int a[20];
double solve(int t, int x, int y){
	if(dp[t][x][y]>-0.5){
		return dp[t][x][y];
	}
	if((x^y)==((1<<n)-1)){
		int sx=0, sy=0;
		for(int i=0; i<n; i++){
			if(x&(1<<i)) sx+=a[i];
			else sy+=a[i];
		}
		if(sx>=sy) return dp[t][x][y]=0;
		else return dp[t][x][y]=1;
	}
	if(t==0){
		double mn=1;
		for(int i=0; i<n; i++){
			if(x&(1<<i) || y&(1<<i)) continue;
			double p=1.0/a[i];
			double mx=0;
			for(int j=0; j<n; j++){
				if(x&(1<<j) || y&(1<<j)) continue;
				double q=1.0/a[j];
				mx=max(mx, p/(1-(1-p)*(1-q))*solve(1, x^(1<<i), y)+(1-p)*q/(1-(1-p)*(1-q))*solve(0, x, y^(1<<j)));
			}
			mn=min(mn, mx);
		}
		return dp[t][x][y]=mn;
	}else{
		double mx=0;
		for(int i=0; i<n; i++){
			if(x&(1<<i) || y&(1<<i)) continue;
			double p=1.0/a[i];
			double mn=1;
			for(int j=0; j<n; j++){
				if(x&(1<<j) || y&(1<<j)) continue;
				double q=1.0/a[j];
				mn=min(mn, q*(1-p)/(1-(1-p)*(1-q))*solve(1, x^(1<<j), y)+p/(1-(1-p)*(1-q))*solve(0, x, y^(1<<i)));
			}
			mx=max(mn, mx);
		}
		return dp[t][x][y]=mx;
	}
}
int main()
{
	cin>>n;
	for(int i=0; i<n; i++) cin>>a[i];
	for(int i=0; i<(1<<n); i++){
		for(int j=0; j<(1<<n); j++){
			dp[0][i][j]=dp[1][i][j]=-1;
		}
	}
	printf("%.7lf\n", solve(1, 0, 0));
	return 0;
}