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

const int MAXN=100005;

int n=0;
double x[MAXN];

int main()
{
//ios::sync_with_stdio(false);
//cin.tie(NULL);
//cout.tie(NULL);
freopen("triangles.in","r",stdin);
freopen("triangles.out","w",stdout);

cin>>n;
for(int i=0;i<n;i++)
{
    scanf("%lf",&x[i]);
}
sort(x,x+n);
long double ans=0;
int k=0;
if(n%2==1) k=1;
for(int i=0;;i++)
{
    if(i+k>n-i-1) break;
    ans+=sqrt(x[i+k]*x[i+k]+x[n-i-1]*x[n-i-1]);
}
cout<<fixed<<setprecision(15)<<ans<<endl;
return 0;
}