#include <bits/stdc++.h>
#define endl '\n'
using namespace std;

int main ()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cout << fixed << setprecision(10);

    freopen("triangles.in", "r", stdin);
    freopen("triangles.out", "w", stdout);

    int n;
    scanf("%d",&n);

    vector <double> v(n);
    for (int i = 0; i < n; i++)
        scanf("%lf",&v[i]);

    sort(v.begin(), v.end());

    if (v.size() % 2)
    {
        v.erase(v.begin());
        n--;
    }

    double ans = 0;

    for (int i = 0; i < n/2 ; i++)
    {
        ans += sqrt(v[i]*v[i] + v[n-i-1]*v[n-i-1]);
    }

    cout << ans << endl;

    return 0;
}