//我的总是RE有哪位能帮我看看近段时间做这类题贡献了无数RE




#include<stdio.h>
#include<string.h>
#include<iostream>
#include<cmath>
#define inf 0x3fffffff
using namespace std;
double map[105][105];
typedef struct Node{
    double x,y,z;
    double r;
}node;
node no[105];
double prim(int n)
{
    int visit[30]={0};
    double dis[30];
    double sum,min;
    int i,j,k;
    sum=0;
    for(i=1;i<=n;++i)
        dis[i]=map[1][i];
    visit[1]=1;
    for(i=2;i<=n;++i)
    {
        min=inf;
        k=1;
        for(j=1;j<=n;++j)
        {
            if(!visit[j]&&min>dis[j])
            {
                min=dis[j];
                k=j;
            }
        }
        visit[k]=1;
        if(min!=inf)
            sum+=min;
        for(j=1;j<=n;++j)
        {
            if(!visit[j]&&dis[j]>map[k][j])
                dis[j]=map[k][j];
        }
    }

    return sum;
}

int main()
{
    int n,len,k,i,j;

    while(scanf("%d",&n),n)
    {
        memset(map,inf,sizeof(map));
        for(int i=1;i<=n;i++)map[i][i]=0;
        for(i=1;i<=n;++i)
        {
            double x,y,z;double r;
            scanf("%lf%lf%lf%lf",&no[i].x,&no[i].y,&no[i].z,&no[i].r);
        }
        for(int i=1;i<=n;i++)
        for(int j=i+1;j<=n;j++){

                double d;
                    node a=no[i],b=no[j];
                    d=sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z));
                if(d > no[i].r + no[j].r)
                {
                    map[i][j] = map[j][i] = d - no[i].r - no[j].r;
                }
                else
                {
                    map[i][j] = map[j][i] = 0;
                }

        }
        double answer;
        answer=prim(n);
        if(abs(answer-0)<0.0001)cout<<"0.00"<<endl;
        else printf("%.3lf\n",answer);

    }
    return 0;
}