#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
#include <algorithm>

typedef unsigned long long ull;


std::vector <int> vec;
long double sum = 0.0;

void sift_up(int i);
void sift_down(int i);

void push(int tmp) {
    vec.push_back(tmp);
    int size = (int)(vec.size())-1;
    sift_up(size);
}

void sift_up(int i) {
    int p = i / 2;
    if(vec[p] > vec[i]) {
        std::swap(vec[i], vec[p]);
        sift_up(p);
    } else {
        return;
    }
}

void sift_down(int i) {
    int ch1, ch2;
    ch1 = i*2+1;
    ch2 = i*2+2;
    if(ch1 > vec.size()-1) return;
    if(ch1 == vec.size()-1) ch2 = ch1;
    int im = vec[ch1] < vec[ch2] ? ch1 : ch2;
    if(vec[im] < vec[i]) {
        std::swap(vec[im], vec[i]);
        sift_down(im);
    } else {
        return;
    }
}

int pop(){
    int head = vec[0];
    vec[0] = vec.back();
    vec.pop_back();
    sift_down(0);
    return head;
}

int main()
{

    int n;
    std::cin >> n;
    int tmp;
    for(int i = 0; i < n;i++){
        std::cin >> tmp;
        push(tmp);
    }

    int tmp1;
    int tmp2;
    int tmp3;

    while(vec.size() > 1) {
        tmp1 = pop();
        tmp2 = pop();
        tmp3 = tmp1 + tmp2;
        sum += tmp3/20.0;
        push(tmp3);
    }

    std::cout << std::fixed << std::setprecision(2) << sum << std::endl;
}