#include <bits/stdc++.h>
#define GET_MACRO(_1,_2,_3,_4,_5,_6,_7,_8,NAME,...) NAME
#define pr(...) cerr<< GET_MACRO(__VA_ARGS__,pr8,pr7,pr6,pr5,pr4,pr3,pr2,pr1)(__VA_ARGS__) <<endl
#define pr1(a) (#a)<<"="<<(a)<<" "
#define pr2(a,b) pr1(a)<<pr1(b)
#define pr3(a,b,c) pr1(a)<<pr2(b,c)
#define pr4(a,b,c,d) pr1(a)<<pr3(b,c,d)
#define pr5(a,b,c,d,e) pr1(a)<<pr4(b,c,d,e)
#define pr6(a,b,c,d,e,f) pr1(a)<<pr5(b,c,d,e,f)
#define pr7(a,b,c,d,e,f,g) pr1(a)<<pr6(b,c,d,e,f,g)
#define pr8(a,b,c,d,e,f,g,h) pr1(a)<<pr7(b,c,d,e,f,g,h)
#define prArr(a) {cerr<<(#a)<<"={";int i=0;for(auto t:(a))cerr<<(i++?", ":"")<<t;cerr<<"}"<<endl;}
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;
const Int INF = (1LL<<60)+1e9; // ~ 1.15 * 1e18
const Int mod = (1e9)+7;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int,Int>;
template<class T> T Max(T &a,T b){return a=max(a,b);}
template<class T> T Min(T &a,T b){return a=min(a,b);}
template<class T1, class T2> ostream& operator<<(ostream& o,pair<T1,T2> p){return o<<"("<<p.first<<","<<p.second<<")";}
template<class T1, class T2, class T3> ostream& operator<<(ostream& o,tuple<T1,T2,T3> t){
  return o<<"("<<get<0>(t)<<","<<get<1>(t)<<","<<get<2>(t)<<")";}
template<class T1, class T2> istream& operator>>(istream& i,pair<T1,T2> &p){return i>>p.first>>p.second;}
template<class T> ostream& operator<<(ostream& o,vector<T> a){Int i=0;for(T t:a)o<<(i++?" ":"")<<t;return o;}
template<class T> istream& operator>>(istream& i,vector<T> &a){for(T &t:a)i>>t;return i;}
//INSERT ABOVE HERE


class UF{
public:
  Int V;
  vector<Int> par,rnk,sz;
  UF(){}
  UF(Int V):V(V),par(V),rnk(V,0),sz(V,1){for(Int i=0;i<V;i++)par[i]=i;}

  Int find(Int x){
    assert(x < V);
    if(par[x]==x)return x;
    return par[x]=find(par[x]);
  }

  void unite(Int x,Int y){
    x=find(x), y=find(y);
    if(x==y)return;
    if(rnk[x]<rnk[y])par[x]=y, sz[y] += sz[x];
    else{
      par[y]=x;
      sz[x] += sz[y];
      if(rnk[x]==rnk[y])rnk[x]++;
    }
  }

  bool same(Int x,Int y){return find(x)==find(y);}

  Int size(Int x){return sz[find(x)];}
};

signed main(){
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(3);

  while(1){
    Int N;
    cin>>N;
    if(N == 0) break;

    using T = tuple<Double, Double, Double, Double>;
    vector<T> A(N);
    for(Int i=0;i<N;i++){
      Double x, y, z, r;
      cin>>x>>y>>z>>r;
      A[i] = T(x, y, z, r);
    }

    auto calcDis=[&](T s, T t){
      Double x, y, z, r; tie(x, y, z, r) = s;
      Double a, b, c, d; tie(a, b, c, d) = t;
      Double dis = sqrt((x - a) * (x - a) + (y - b) * (y - b) + (z - c) * (z - c));
      Double res = max((Double)0, (dis - (r + d)));
      return res;
    };

    using E = tuple<Double, Int, Int>;
    vector<E> edge;
    for(Int i=0;i<N;i++)
      for(Int j=i+1;j<N;j++){
        Double cost = calcDis(A[i], A[j]);
        edge.emplace_back(cost, i, j);
      }

    sort(edge.begin(), edge.end());
    UF uf(N);
    Double ans = 0;
    for(auto e:edge){
      Double c;
      Int a, b; tie(c, a, b) = e;
      if(uf.same(a, b)) continue;
      uf.unite(a, b);
      ans += c;
    }
    cout<<ans<<endl;
  }

  return 0;
}



Measured memory_bytes: 3436