#include <iostream>
#include <cstring>
#include <cmath>

using namespace std;


double dist(int x1,int y1,int x2,int y2)
{
  return sqrt( (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2) );
}
int main()
{
    int n,i,j;
    int x[101],y[101];
    bool vis[101];
    double res=0.0,najmalo_dist;
    int cnt,teme;
    memset(vis,false,sizeof(vis));

    cin>>n;


    for(i=1;i<=n;i++)
    {
      cin>>x[i]>>y[i];
    }

   cnt=1;
   vis[1]=true;

double t;
   while(cnt<n)
   {
     najmalo_dist=1000000.0; //very big double
     teme=-1;
     for(i=1;i<=n;i++) //za poseteni
     {
        if(vis[i]==false) continue;

        for(j=1;j<=n;j++) //za neposeteni
        {
           if(vis[j]==true) continue;
           t=dist(x[i],y[i],x[j],y[j]);

          if(t<najmalo_dist)
          {
             najmalo_dist=t;
             teme=j;
          }

        }
     }

     res+=najmalo_dist;
     vis[teme]=true;
     cnt++;
   }//end_while

 int r=res*100;
 cout<<r/100<<"."<<(r/10)%10<<r%10<<endl;
    return 0;
}