#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;

#define MAX 100

int main(void){
  int n;
  double x[MAX],y[MAX],z[MAX],r[MAX];
  double dist[MAX][MAX];
  bool connect[MAX];
  int count;
  int cur_trg;
  double cur_dist;
  double ans;
  while(true){
    cin >> n;
    if(n==0) break;
    for(int i=0;i<n;i++)
      cin >> x[i] >> y[i] >> z[i] >> r[i];
    for(int i=0;i<n;i++){
      for(int j=i+1;j<n;j++){
	dist[i][j] = (x[i]-x[j])*(x[i]-x[j])
	              +(y[i]-y[j])*(y[i]-y[j])
                      +(z[i]-z[j])*(z[i]-z[j]);
	dist[i][j] = sqrt(dist[i][j]);
        dist[i][j] -= r[i]+r[j];
	if(dist[i][j]<0) dist[i][j] = 0;
      }
    }
    for(int i=0;i<n;i++){
      for(int j=0;j<i;j++){
	dist[i][j] = dist[j][i];
      }
    }
    
    for(int i=0;i<n;i++)
      connect[i] = false;
    
    connect[0]=true;
    ans = 0;
    for(count = 1;count!=n;count++){
      cur_dist = 10000;
      for(int i=0;i<n;i++){
	if(connect[i]) continue;
	for(int j=0;j<n;j++){
	  if(!connect[j]) continue;
	  if(dist[i][j] >= cur_dist) continue;
	  cur_dist = dist[i][j];
	  cur_trg  = i;
	}
      }
      connect[cur_trg] = true;
      ans += cur_dist;
    }
    printf("%.3f\n",ans);
  }
  return 0;
}