#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 1000000001

int N;
vector<int> A;
vector<vector<double>> P;
int t=  0;
double dp[1024][102][102][2];

double get(int state,int s,int t,int now){
	if(s>=101)return 1.0;
	if(t>=100)return 0.0;
	if(state==(1<<N)-1){
		if(s>t)return 1.0;
		else return 0.0;
	}
	
	//static vector dp(1<<N,vector(102,vector(102,vector<double>(2,-100.0))));
	if(dp[state][s][t][now]>-1.0)return dp[state][s][t][now];

	double ret;
	if(now==0)ret = 0.0;
	else ret = 1.0;
	int ind = 0;
	for(int i=0;i<N;i++){
		if((state>>i)&1)continue;
		double m;
		if(now==0)m=1.0;
		else m = 0.0;
		for(int j=0;j<N;j++){
			if((state>>j)&1)continue;
			double p = P[i][j];
			if(now==0){
				m = min(m,get(state|(1<<i),s+A[i],t,1)*p + get(state|(1<<j),s,t+A[j],0)*(1.0-p));
			}
			else{
				m = max(m,get(state|(1<<i),s,t+A[i],0)*p + get(state|(1<<j),s+A[j],t,1)*(1.0-p));
			}
		}
		//cout<<state<<','<<now<<','<<m<<endl;
		if(now==0)ret = max(ret,m);
		else ret = min(ret,m);
	}
	
	dp[state][s][t][now] = ret;
	return ret;
}

int main(){
	
	for(int i=0;i<1024;i++){
	for(int j=0;j<102;j++){
		for(int k=0;k<102;k++){
			for(int l=0;l<2;l++)dp[i][j][k][l] = -100.0;
		}
	}
}
	
	
	cin>>N;
	A.resize(N);
	for(int i=0;i<N;i++)cin>>A[i];
	
	P.resize(N,vector<double>(N,0.0));
	
	for(int i=0;i<N;i++){
		for(int j=0;j<N;j++){
			if(A[i]==1){
				P[i][j]=1.0;
				continue;
			}
			if(A[j]==1){
				P[i][j]=1.0/A[i];
				continue;
			}
			for(int k=1;k<=1000;k+=2){
				P[i][j] += pow(1.0/(double)A[i],1) * pow(1.0-(1.0/(double)A[i]),k/2) * pow(1.0-(1.0/(double)A[j]),k/2);
			}
		}
	}
	//cout<<'a'<<endl;
	cout<<fixed<<setprecision(10)<<get(0,0,0,0)<<endl;

	return 0;
}