#include <stdio.h>

 #include <math.h>

 #include <string.h>

 const int inf=<<;

 const double eps=1e-;

 const int maxn=;

 double sum,Map[maxn][maxn],dis[maxn];

 int vis[maxn];

 struct point

 {

     double x,y,z,r;

 };

 void prim(int n)

 {

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

         dis[i]=inf;

     dis[]=;

     sum=;

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

     {

         double Min=inf;

         int pos=;

         for (int j = ; j <= n; j++)

         {

             if (!vis[j]&&dis[j] < Min)

             {

                 Min = dis[j];

                 pos = j;

             }

         }

         if (Min==inf)

             return;

         vis[pos] = ;

         sum+=Min;

         for (int j = ; j <= n; j++)

         {

             if (!vis[j]&&dis[j] > Map[pos][j])

                 dis[j] = Map[pos][j];

         }

     }

 }

 void init()

 {

     sum = ;

     memset(vis,,sizeof(vis));

     memset(Map,,sizeof(Map));

 }

 double dist(point &a,point &b)

 {

     return (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z);

 }

 int main()

 {

     int n;

     while(~scanf("%d",&n)&&n)

     {

         point a[];

         init();

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

         {

             scanf("%lf%lf%lf%lf",&a[i].x,&a[i].y,&a[i].z,&a[i].r);

         }

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

         {

             for (int j = ; j <= n; j++)

             {

                 double d = sqrt(dist(a[i],a[j]));

                 if (d-(a[i].r+a[j].r)>eps)

                     Map[i][j] = d-a[i].r-a[j].r;

                 else

                     Map[i][j] = ;

             }

         }

         prim(n);

         printf("%.3f\n",sum);

     }

     return ;

 }