#include<iostream>
#include<cstdio>
#include<algorithm>
#include<iomanip>
#include<math.h>
#define MAXN 100002
#define int long long
using namespace std;
int n;
double arr[MAXN], ans;
signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout<<fixed;
    cout<<setprecision(10);
    freopen("triangles.in", "r", stdin);
    freopen("triangles.out", "w", stdout);
    cin>>n;
    for(int i = 0; i < n; i ++)
    {
        cin>>arr[i];
    }
    sort(arr, arr + n);
    for(int i = 0; i < n / 2; i ++)
    {
        ans += sqrt(arr[i] * arr[i] + arr[n - i - 1] * arr[n - i - 1]);
    }
    cout<<ans<<endl;
    return 0;
}