#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rep(i,a,b) for(int i=(a);i>=(b);--i)
//#define int long long 
using namespace std;
inline int read()
{
    char c=getchar();int x=0;bool f=0;
    for(;!isdigit(c);c=getchar())f^=!(c^45);
    for(;isdigit(c);c=getchar())x=(x<<1)+(x<<3)+(c^48);
    if(f)x=-x;return x;
}

#define fi first
#define se second
#define pb push_back
#define mkp make_pair
typedef pair<int,int>pii;
typedef vector<int>vi;

#define maxn 300005
#define inf 0x3f3f3f3f

int n;
double f[1<<22|5];
double wa[33],wb[33];
int a[33],m;

double solve(int s)
{
	if(wb[m-1]>=wa[m-1])return wa[m-1];
	double k=0,b=0;
	k+=1.0/(wa[m-1]-wb[m-1]);
	Rep(i,m-2,0){
		if(k*(wa[i+1]-wa[i])+b>1) return wa[i+1]-(1-b)/k;
		b+=k*(wa[i+1]-wa[i]);
		if(wb[i]>=wa[i])return wa[i];
		k+=1.0/(wa[i]-wb[i]);
	}
	return wa[0]-(1-b)/k;
}

signed main()
{
	n=read();
	For(i,0,n-1)a[i]=read();
	sort(a,a+n);
	int mxs=(1<<n);
	For(s,0,mxs-1){
		if(__builtin_popcount(s)==1)continue;
		m=0;
		For(i,0,n-1)
			if(s>>i&1)
				wa[m]=a[i],wb[m]=f[s^(1<<i)],++m;
		f[s]=solve(m);
	}
	printf("%.10lf\n",f[mxs-1]);
	return 0;
}