#include<bits/stdc++.h>

using namespace std;

int n;
double a[100005];

int main()
{

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

    cin>>n;
    for(int i=0; i<n; i++)
    {
        scanf("%lf", &a[i]);
    }
    sort(a, a+n);
    int i=0, j=n-1;
    if(n%2) i++;
    double res=0;
    for(; i<j; i++, j--) res+=sqrt(a[i]*a[i]+a[j]*a[j]);
    cout<<fixed<<setprecision(9)<<res<<endl;
    return 0;
}