#include<cstdio>

 #include<cstring>

 #include<cmath>

 #include<algorithm>

 using namespace std;

 const double eps=1e-;

 const int inf=<<;

 int cmp(double x)

 {

     if(fabs(x)<eps) return ;

     if(x>) return ;

     return -;

 }

 const double pi=acos(-1.0);

 inline double sqr(double x)

 {

     return x*x;

 }

 inline double Sqrt(double a)

 {

     return a<=?:sqrt(a);

 }

 struct point

 {

    double x,y,z,r;

    point(){}

    point(double a,double b,double c,double d):x(a),y(b),z(c),r(d){}

 };

 double dis(const point &a,const point &b)

 {

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

 }

 double dist[];

 double diss[][],ans;

 bool vis[];

 bool prime(int n)

 {

     memset(vis,,sizeof(vis));

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

         dist[i]=inf;

     ans=;dist[]=;

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

         double temp=inf;

         int k=;

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

         {

             if(!vis[j]&&dist[j]<temp)

             {

                 temp=dist[j];

                 k=j;

             }

         }

         if(temp==inf) return false;

         vis[k]=true;

         ans+=temp;

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

         {

             if(!vis[j]&&dist[j]>diss[k][j])

             {

                 dist[j]=diss[k][j];

             }

         }

     }

     return true;

 }

 int main()

 {

     int n;

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

     {

         point a[];

         memset(diss,,sizeof(diss));

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

         {

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

         }

         memset(diss,,sizeof(diss));

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

         {

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

             {

                 if(dis(a[i],a[j])-a[i].r-a[j].r<=)

                 diss[i][j]=;

                 else if(dis(a[i],a[j])-a[i].r-a[j].r>eps)

                 diss[i][j]=dis(a[i],a[j])-a[i].r-a[j].r;

             }

         }

         prime(n);

         printf("%.3lf\n",ans);

     }

     return ;

 }