#include <iostream>
#include <vector>
#include <cmath>
#include <climits>
#include <map>
#include <utility>
#include <cstdio>

using namespace std;

struct POS
{
  double x, y, z;
  double Distance(const POS& rh)const{
    return sqrt((x - rh.x) * (x - rh.x) +
		(y - rh.y) * (y - rh.y) +
		(z - rh.z) * (z - rh.z));
  }
};

struct SPHERE
{
  POS p;
  double r;
};

const double EPSIRON = 0.000000001;

int CONNECT[100][100];
int VISITED[100];

bool DFS(int from, int to, const vector<vector<int> >& graph)
{
  if (VISITED[from]){
    return false;
  }
  VISITED[from] = true;
  if (CONNECT[from][to] || from == to){
    return true;
  }

  const vector<int>& nodes = graph[from];
  for (vector<int>::const_iterator it = nodes.begin();
       it != nodes.end(); ++it){
    if (DFS(*it, to, graph)){
      CONNECT[*it][to] = true;
      CONNECT[to][*it] = true;
      CONNECT[from][to] = true;
      CONNECT[to][from] = true;
      CONNECT[*it][from] = true;
      CONNECT[from][*it] = true;
      return true;
    }
  }

  return false;
}

bool IsConnected(int from, int to, const vector<vector<int> >& graph)
{
  memset(VISITED, 0, sizeof(VISITED));
  return DFS(from, to, graph);
}

main()
{
  int n;
  while (cin >> n && n){
    SPHERE v[n];
    vector<vector<int> > graph(n);
    memset(CONNECT, 0, sizeof(CONNECT));

    multimap<double, pair<int, int> > open;
    for (int i = 0; i < n; ++i){
      SPHERE& s = v[i];
      cin >> s.p.x >> s.p.y >> s.p.z >> s.r;
      //cerr << s.p.x << " " << s.p.y << " " << s.p.z << " " << s.r;
      for (int j = 0; j < i; ++j){
	double d = v[i].p.Distance(v[j].p);
	double f = d - v[i].r - v[j].r;
	if (f > - EPSIRON){
	  open.insert(make_pair(f, make_pair(i, j)));
	  //cerr << f << " " << i << " " << j << endl;;
	  //dist[i][j] = dist[j][i] = f;
	} else {
	  graph[i].push_back(j);
	  graph[j].push_back(i);
	  CONNECT[i][j] = true;
	  CONNECT[j][i] = true;
	  //cerr << i << " " << j << endl;
	}
      }
    }
    //cerr << "hoge" << endl;

    bool is_ok = true;

    for (int i = 1; i < n; ++i){
      is_ok &= IsConnected(0, i, graph);
    }
    
    if (is_ok){
      printf("0.000\n");
      continue;
    }

    double answer = 0.0;
    is_ok = false;
    while (!is_ok){
      double d = open.begin()->first;
      int from = open.begin()->second.first;
      int to = open.begin()->second.second;
      open.erase(open.begin());
      //cerr << d << " " << from << " " << to << endl;
      if (IsConnected(from, to, graph)){
	continue;
      }

      CONNECT[from][to] = true;
      CONNECT[to][from] = true;
      graph[from].push_back(to);
      graph[to].push_back(from);

      //cerr << "hoge" << endl;

      answer += d;
      
      is_ok = true;
      for (int i = 1; i < n; ++i){
	is_ok &= IsConnected(0, i, graph);
      }
    }

    printf("%.03lf\n", answer);
  }
}