#include<bits/stdc++.h>
#define endl '\n'
#define eps 0.00000000001
using namespace std;
double x[100050];
bool cmp(double a, double b)
{
    return a-b>eps;
}
int main()
{
    freopen("triangles.in","r",stdin);
    freopen("triangles.out","w",stdout);
    /*ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
*/
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        scanf("%lf",&x[i]);
    }

    sort(x,x+n,cmp);
    if(n&1)n--;
    double otg=0;
    for(int i=0;i<n/2;i++)
    {
        otg+=sqrt(x[i]*x[i]+x[n-i-1]*x[n-i-1]);
    }
    cout<<fixed<<setprecision(10)<<otg<<endl;
    return 0;
}