#include <iostream>
#include <cstdio>
#include <map>
#include <cmath>

using namespace std;

struct Pos {
  double x, y, z;
  Pos() {}
  Pos(double xx, double yy, double zz) : x(xx), y(yy), z(zz) {}
  double dist(const Pos& b) {
    double dx = x - b.x;
    double dy = y - b.y;
    double dz = z - b.z;
    return sqrt(dx * dx + dy * dy + dz * dz);
  }
};

int n;
Pos p[110];
double r[110];
double dist[110][110];

double Solve() {
  double ans = 0;
  bool v[110];
  memset(v, 0, sizeof(v));
  multimap<double, int> edge;
  edge.insert(make_pair(0.0, 0));
  while(!edge.empty()) {
    double d = edge.begin()->first;
    int c = edge.begin()->second;
    edge.erase(edge.begin());
    if(v[c])
      continue;
    v[c] = true;
    ans += d;
    for(int i = 0; i < n; ++i)
      edge.insert(make_pair(dist[c][i], i));
  }
  return ans;
}

int main() {
  while(cin >> n && n) {
    for(int i = 0; i < n; ++i) {
      double x,y,z;
      cin >> x >> y >> z >> r[i];
      p[i] = Pos(x,y,z);
    }
    for(int i = 0; i < n; ++i)
      for(int j = 0; j < n; ++j) {
	double d = p[i].dist(p[j]) - r[i] - r[j];
	if(d < 0) d = 0.0;
	dist[i][j] = d;
      }
    double ans = Solve();
    printf("%.3f\n", ans);
  }
}