#include<iostream>
#include<cmath>
#include<vector>
#include<algorithm>
#include<cstdio>
using namespace std;
int x[5001],y[5001];
const double INF=100000000;
double dest(int x1,int y1,int x2,int y2)
{
    return sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
}
bool used[5001];
double d[5001];
int main()
{
    freopen("unionday.in","r",stdin);
    freopen("unionday.out","w",stdout);
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        cin>>x[i]>>y[i];
    }
    for(int i=0;i<n;i++) d[i]=INF;
    d[0]=0;
    double ans=0;
    for(int i=0;i<n;i++)
    {
        double best=INF;
        int cur=0;
        for(int j=0;j<n;j++)
        {
            if(d[j]<best && !used[j])
            {
                cur=j;
                best=d[j];
            }
        }
        used[cur]=true;
        ans+=best;
        for(int j=0;j<n;j++)
        {
           d[j]=min(d[j],dest(x[cur],y[cur],x[j],y[j]));
        }
    }
    cout.precision(8);
    cout<<fixed<<ans<<endl;
}