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

const int maxn = 22;
typedef double db;
typedef long long ll;

int c[maxn],tot=0;
db a[maxn],b[maxn];
db dp[1<<maxn];

db solve(int n){
	db sumder=0,sump=0;
	if(a[1]<=b[1])return a[1];
	sumder=1./(a[1]-b[1]);
	for(int i=2;i<=n;++i){
		db deta=a[i-1]-a[i];
		db ad=deta*sumder;
		if(sump+ad>1)return a[i-1]-(1-sump)/sumder;
		if(a[i]<=b[i])return a[i];
		sumder+=1./(a[i]-b[i]);
		sump+=ad; 
	}
	return a[n]-(1-sump)/sumder;
}
int main(){
	int n;
	scanf("%d",&n);
	for(int i=0;i<n;++i)scanf("%d",&c[i]);
	sort(c,c+n);
	for(int i=1;i<(1<<n);++i){
		tot=0;
		for(int j=n-1;j>=0;--j){
			if(!((i>>j)&1))continue;
			a[++tot]=c[j];
			b[tot]=dp[i^(1<<j)];
		}
		dp[i]=solve(tot);
	} 
	printf("%.12lf\n",dp[(1<<n)-1]);
}