/*

   最小生成树 + 几何判断

   Kruskal      球心之间的距离 - 两个球的半径 < 0 则说明是覆盖的！此时的距离按照0计算

 */

 #include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<cmath>

 #include<algorithm>

 using namespace std;

 int f[];

 struct ball{

    double x, y, z, r;

 };

 struct connect{

    double dist;

    int a, b;

 };

 connect c[];

 ball b[];

 bool cmp(connect a, connect b){

    return a.dist < b.dist;

 }

 int n;

 int getFather(int x){

    return x==f[x] ? x : f[x]=getFather(f[x]);

 } 

 int Union(int a, int b){

     int fa=getFather(a), fb=getFather(b);

     if(fa!=fb){

         f[fa]=fb;

         return ;

     }

     return ;

 }

 int main(){

    int i, j;

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

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

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

       int cnt=;

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

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

              double d = sqrt((b[i].x-b[j].x)*(b[i].x-b[j].x) + (b[i].y-b[j].y)*(b[i].y-b[j].y) + (b[i].z-b[j].z)*(b[i].z-b[j].z))

                         - (b[i].r + b[j].r);

                c[cnt].dist= d< ? : d;

                c[cnt].a=i;

                c[cnt++].b=j;

          }

        sort(c, c+cnt, cmp);

        double minSum=0.0;

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

           f[i]=i;

        for(i=; i<cnt; ++i){

           if(Union(c[i].a, c[i].b))

              minSum+=c[i].dist;

        }

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

    }

    return ;

 }