#include<cstdio>

#include<cstring>

#include<algorithm>

#include<queue>

#include<cmath>

using namespace std;

const int M=1e5+;

const double inf=;

int read(){

    int ans=,f=,c=getchar();

    while(c<''||c>''){if(c=='-') f=-; c=getchar();}

    while(c>=''&&c<=''){ans=ans*+(c-''); c=getchar();}

    return ans*f;

}

int n,x[M],y[M],vis[M];

double ans,d[M];

double G_d(int a,int b){return sqrt(1.0*(x[a]-x[b])*(x[a]-x[b])+1.0*(y[a]-y[b])*(y[a]-y[b]));}

void prm(){

    vis[]=; d[]=0.0;

    for(int i=;i<=n;i++) d[i]=G_d(,i);

//    for(int i=1;i<=n;i++) printf("%.2lf ",d[i]); puts("");

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

        int id,mn=inf;

        for(int j=;j<=n;j++)if(!vis[j]&&d[j]<mn) mn=d[j],id=j;

        vis[id]=;

        for(int j=;j<=n;j++)if(!vis[j]) d[j]=min(d[j],G_d(id,j));

    }

}

int main(){

    n=read();

    for(int i=;i<=n;i++) x[i]=read(),y[i]=read();

    prm();

    for(int i=;i<=n;i++) ans+=d[i];

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

    return ;

}