#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
long long a[100002],x=0;
int n;
int cmp(long long p1,long long p2)
{
    return (p1>p2);
}
void f2()
{
    if(n<2){return;}
    x+=a[0];
    pop_heap(a,a+n,cmp);
    --n;
    x+=a[0];
    pop_heap(a,a+n,cmp);
    a[n-1]+=a[n];
    push_heap(a,a+n,cmp);
    f2();
}
int main()
{
    int i;
    scanf("%d",&n);
    for(i=0;i<n;i++)
    {
        //scanf("%d",&a[i]);
        cin>>a[i];
    }
    make_heap(a,a+n,cmp);
    f2();
    x=x*5;
    cout<<x/100<<"."<<x%100<<endl;
    return 0;
}
