#include <bits/stdc++.h>
#define MOD 1000000007LL
using namespace std;
typedef long long ll;
typedef pair<int,int> P;

int n;
int a[11];
double dp[2][60000];
bool flag[2][60000];

bool used(int pos,int bit){
	for(int i=0;i<pos;i++){
		bit/=3;
	}
	if(bit%3!=0)return true;
	return false;
}

double solve(int v,int bit){
	if(flag[v][bit]){
		return dp[v][bit];
	}
	flag[v][bit]=true;
	double ans=0.0;
	if(v==1){
		ans=1.0;
	}
	int kg=1;
	for(int i=0;i<n;i++){
		if(used(i,bit)){
			kg*=3;
			continue;
		}
		double val=1.0;
		if(v==1){
			val=0.0;
		}
		double v1=1.0/(double)a[i]*solve(1-v,bit+(kg)*(1+v));
		int kg2=1;
		for(int j=0;j<n;j++){
			if(used(j,bit)){
				kg2*=3;
				continue;
			}
			double v2=(1.0-1.0/(double)a[i])*(1.0/(double)a[j])*solve(v,bit+kg2*(2-v));
			double pi=(1.0-1.0/(double)a[i])*(1.0-1.0/(double)a[j]);
			pi=1.0-pi;
			double v3=(v1+v2)/pi;
			//printf("%d %d %d %d %.5f %.5f %.5f %.10f\n",v,bit,i,j,v1,v2,pi,v3);
			if(v==0){
				val=min(val,v3);
			}else{
				val=max(val,v3);
			}
			kg2*=3;
		}
		if(v==0){
			ans=max(ans,val);
		}else{
			ans=min(ans,val);
		}
		kg*=3;
	}
	//printf("%d %d ans= %.10f\n",v,bit,ans);
	return dp[v][bit]=ans;
}

int main(void){
	scanf("%d",&n);
	for(int i=0;i<n;i++){
		scanf("%d",&a[i]);
	}
	for(int i=0;i<(1<<n);i++){
		int val=0;
		int bit=0;
		int k=1;
		for(int j=0;j<n;j++){
			if((i>>j)&1){
				bit+=k;
				val+=a[j];
			}else{
				bit+=2*k;
				val-=a[j];
			}
			k*=3;
		}
		if(val>0){
			dp[0][bit]=1.0;
			dp[1][bit]=1.0;
			flag[0][bit]=true;
			flag[1][bit]=true;
		}else{
			dp[0][bit]=0.0;
			dp[1][bit]=0.0;
			flag[0][bit]=true;
			flag[1][bit]=true;
		}
	}
	printf("%.10f\n",solve(0,0));
	return 0;
}