#include<bits/stdc++.h>
using namespace std;
int n;
vector<double> v;
bool cmp(double c, double d)
{
    return c > d;
}
int main()
{
	/*ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);*/
	//cin >> n;
	scanf("%d", &n);
	for (int i = 0; i < n; ++i){
        double a;
        //cin >> a;
        scanf("%d", &a);
        v.push_back(a);
	}
	sort(v.begin(), v.end(), cmp);
	double ans = 0;
	for (int i = 0; i < n / 2; ++i){
        ans += sqrt(v[i] * v[i] + v[i + n/2] * v[i + n/2]);
        //cout << v[i] << " " << v[n - i - 1]<<endl;
    }
    //cout << ans << "\n";
    printf("%.9f\n", ans);
return 0;
}