#include <bits/stdc++.h>
using namespace std;

vector<double> v;

int main()
{
    freopen("triangles.in", "r", stdin);
    freopen("triangles.out", "w", stdout);
    int n, i;
    double p;
    scanf("%d", &n);
    for(i=1;i<=n;i++) {
        scanf("%lf", &p);
        v.push_back(p);
    }
    sort(v.begin(), v.end());
    double ans = 0;
    if(n%2 == 0) {
        for(i=0;i<v.size()/2;i++) {
            ans+= sqrt(v[i]*v[i] + v[v.size()-i-1]*v[v.size()-i-1]);
        }
    }
    else {
        for(i=1;i<=v.size()/2;i++) {
            ans+= sqrt(v[i]*v[i] + v[v.size()-i]*v[v.size()-i]);
        }
    }
    printf("%.9lf\n", ans);

    return 0;
}