// 01:33-2:06

#include<iostream>
#include<map>
#include<set>
#include<vector>
#include<valarray>

#define EPS 1.e-5
#define LE(x, y) ((x) - (y) < EPS)

using namespace std;

typedef valarray<double> xyz;
typedef vector<vector<double> > adj_matrix;

struct station{
  xyz p;
  double r;
  station(){}
  station(const xyz &p, double r):p(p), r(r){}
};

double infty = 9999999999.;


double prim(adj_matrix &m){
  int N = m.size();
  if(N <= 1) return 0.;

  set<int> tobeadded;
  for(int i = 1; i < N; i++){
    tobeadded.insert(i);
  }
  int lastadded = 0;

  vector<double> distances(N, infty);

  double totalweight = 0.;

  for(int i = 0; i < N - 1; i++){
    double distmin = infty;
    int next = -1;
    for(set<int>::iterator it = tobeadded.begin();
        it != tobeadded.end(); ++it){
      double &distnow = distances[*it];
      if(m[lastadded][*it] < distnow){
        distnow = m[lastadded][*it];
      }
      if(distnow < distmin){
        distmin = distnow;
        next = *it;
      }
    }
    if(distmin == infty){
      break;
    }
    totalweight += distances[next];
    tobeadded.erase(next);
    lastadded = next;
  }

  return totalweight;
}

int main(void){
  int N;
  while(cin >> N && N){
    vector<station> stations;
    for(int i = 0; i < N; i++){
      xyz p(3);
      double r;

      cin >> p[0] >> p[1] >> p[2] >> r;

      stations.push_back(station(p, r));
    }

    adj_matrix distance(N, vector<double>(N, 0.));
    for(int i = 0; i < stations.size(); i++){
      distance[i][i] = infty;
      for(int j = i + 1; j < stations.size(); j++){
        xyz diff = stations[i].p - stations[j].p;
        double norm = (diff*diff).sum();
        double abs_ = sqrt(norm) - stations[i].r - stations[j].r;
        if(LE(abs_, 0.)) abs_ = 0.;

        distance[i][j] = abs_;
        distance[j][i] = abs_;
      }
    }

    printf("%.3f\n", prim(distance));
  }
  return 0;
}