#include<iostream>

#include<cstdio>

#include<algorithm>

#include<cstring>

#include<queue>

using namespace std;

int a[];

char s[];

struct node

{

    int w;

    friend bool operator <(node aa, node bb) //<为从大到小排列，>为从小到大排列

    {

        return aa.w > bb.w;

    }

};

int main()

{

    int n;

    while(scanf("%d",&n)!=EOF)

    {

        memset(a, , sizeof(a));

        int num=,len=n;

        for(int i=;i<=n;i++) //题目已知每一种字母有多少个，没已知要自己数

            cin>>a[i];

        priority_queue <node> q;

        for(int i=;i<;i++)

        {

            num+=a[i];

            node b;

            b.w=a[i];

            if(a[i])

                q.push(b);

        }

        int res;

        if(q.size() == )

            res = len;

        else

        {

            res = ;

            while(q.size() > )

            {

                int aa = q.top().w; q.pop();

                int bb = q.top().w; q.pop();

                res += (aa + bb);

                node b;

                b.w = aa + bb;

                q.push(b);

            }

        }

        double temp=double(res)/(double)num;

        printf("%.2lf\n",temp);

    }

    return ;

}