#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rof(i,a,b) for(int i=(a);i>=(b);--i)
using namespace std;
const int Maxn=(1<<22);
const double eps=1e-9;

int n,m,lim,a[25],id[25]; double f[Maxn+5];

int main()
{
    // freopen("1.in","r",stdin);

    cin>>n; For(i,0,n-1) cin>>a[i]; lim=(1<<n)-1; f[0]=0;
    For(s,1,lim)
    {
        double s1=0,s2=0,mx=0; int flg=0; m=0;
        auto Get=[&](){return (s1-1)/s2;};
        For(i,0,n-1) if(s&(1<<i))
        {
            double b=f[s^(1<<i)];
            if(b>a[i]) mx=max(mx,1.0*a[i]);
            else id[++m]=i;
        }
        sort(id+1,id+m+1,[&](int x,int y){return a[x]>a[y];});
        For(_,1,m)
        {
            int i=id[_]; double b=f[s^(1<<i)];
            if(Get()>a[i]) break;
            if(abs(a[i]-b)<=eps) {flg=1,f[s]=max(mx,b); break;}
            s1+=1.0*a[i]/(a[i]-b),s2+=1.0/(a[i]-b);
        } if(!flg) f[s]=max(mx,Get());
    }
    printf("%.9lf\n",f[lim]);
    return 0;
}