#include <iostream>
#include <set>
#include <map>
#include <algorithm>
#include <stdio.h>
struct S{
  double x, y, z, r;
  S(){}
  S(double x_, double y_, double z_, double r_):
    x(x_), y(y_), z(z_), r(r_){}

  static double distance(const S& a, const S & b){
    double dx = a.x - b.x;
    double dy = a.y - b.y;
    double dz = a.z - b.z;
    return std::max(sqrt(dx * dx + dy * dy + dz * dz) - a.r - b.r, 0.0);
  }
  bool operator < (const S & s) const{
    if(x != s.x){return x < s.x;}
    if(y != s.y){return y < s.y;}
    if(z != s.z){return z < s.z;}
    if(r != s.r){return r < s.r;}
  }
};

int main(){
  while(true){
  int n;
  std::cin >> n;
  if(n == 0){break;}
  S ss[n];
  for(int i = 0; i < n; i++){
    double x, y, z, r;
    std::cin >> x >> y >> z >> r;
    ss[i] = (S(x, y, z, r));
  }
  bool include[n];
  memset(include, 0, sizeof(include));
  include[0] = true;
  double all = 0;
  for(int t = 1;  t < n; t++){
    double m = 1e12;
    int mi = 0;
    int mj = 0;
    for(int i = 0; i < n; i++){
      for(int j = 0; j < n; j++){
	if(include[i] != include[j]){
	  if(m > S::distance(ss[i], ss[j])){
	    m =  S::distance(ss[i], ss[j]);
	    mi = i;
	    mj = j;
	  }
	}
      }
    }
    all += m;
    if(include[mi]){
      include[mj] = true;
    }else{
      include[mi] = true;
    }
  }
  char buffer[100];
  sprintf(buffer, "%.3f", all);
  std::cout << buffer << std::endl;
}
}