#include<bits/stdc++.h>

#define rep(i,r) for(int i=1;i<=r;i++)

#define Dis(a,b) (sqrt((x[a]-x[b])*(x[a]-x[b])+(y[a]-y[b])*(y[a]-y[b])))

#define N 5010

int n,fa[N];

double x[N],y[N],dis[N],ans;

bool vis[N];

double min(double a,double b) { return a<b?a:b; }

int main(){

    scanf("%d",&n);

    rep(i,n) scanf("%lf%lf",&x[i],&y[i]);

    std::fill(dis,dis+n+,); dis[]=;

    for(int i=;i<=n;i++){

        int k=; rep(j,n)

        if(!vis[j]&&dis[j]<dis[k]) k=j;

        vis[k]=; ans+=dis[k];

        rep(j,n) dis[j]=min(dis[j],Dis(k,j));

    }

    printf("%.2lf\n",ans); return ;

}