// clang-format off
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define main signed main()
#define loop(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) loop(i, 0, n)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define prec(n) fixed << setprecision(n)
constexpr int INF = sizeof(int) == sizeof(long long) ? 1000000000000000000LL : 1000000000;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979;
template<typename A, typename B> bool cmin(A &a, const B &b) { return a > b ? (a = b, true) : false; }
template<typename A, typename B> bool cmax(A &a, const B &b) { return a < b ? (a = b, true) : false; }
bool odd(const int &n) { return n & 1; }
bool even(const int &n) { return ~n & 1; }
template<typename T = int> T in() { T x; cin >> x; return x; }
template<typename T = int> T in(T &&x) { T z(forward<T>(x)); cin >> z; return z; }
template<typename T> istream &operator>>(istream &is, vector<T> &v) { for (T &x : v) is >> x; return is; }
template<typename A, typename B> istream &operator>>(istream &is, pair<A, B> &p) { return is >> p.first >> p.second; }
template<typename T> ostream &operator<<(ostream &os, const vector<vector<T>> &v) { int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "" : "\n"); return os; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &v) { int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "" : " "); return os; }
template<typename A, typename B> ostream &operator<<(ostream &os, const pair<A, B> &p) { return os << p.first << ' ' << p.second; }
template<typename Head, typename Value> auto vectors(const Head &head, const Value &v) { return vector<Value>(head, v); }
template<typename Head, typename... Tail> auto vectors(Head x, Tail... tail) { auto inner = vectors(tail...); return vector<decltype(inner)>(x, inner); }
// clang-format on

using Weight = double;
struct Edge {
  int src, dst;
  Weight weight;
  Edge(const int &s = 0, const int &d = 0, const Weight &w = 0) : src(s), dst(d), weight(w) {}
};

using Edges = vector<Edge>;
using Array = vector<Weight>;
using Matrix = vector<Array>;

class Graph {
  vector<Edges> g;
  using iterator = vector<Edges>::iterator;
  using const_iterator = vector<Edges>::const_iterator;

public:
  Graph(const int &size = 0) : g(size) {}
  size_t size() const { return g.size(); }
  const Edges &operator[](const int &i) const { return g[i]; }
  void addArc(const int &src, const int &dst, const Weight &w = 1) { g[src].emplace_back(src, dst, w); }
  void addEdge(const int &node1, const int &node2, const Weight &w = 1) {
    addArc(node1, node2, w);
    addArc(node2, node1, w);
  }
  iterator begin() { return g.begin(); }
  const_iterator begin() const { return g.begin(); }
  iterator end() { return g.end(); }
  const_iterator end() const { return g.end(); }
};

class UnionFind {
  vector<int> tree, rank, setSize;

public:
  UnionFind(const int &n) : tree(n), rank(n), setSize(n, 1) { iota(all(tree), 0); }

  int root(const int &x) { return tree[x] == x ? x : tree[x] = root(tree[x]); }

  bool same(const int &a, const int &b) { return root(a) == root(b); }

  bool unite(int a, int b) {
    a = root(a), b = root(b);
    if (a == b) return false;
    if (rank[a] < rank[b]) swap(a, b);
    tree[b] = a;
    setSize[a] += setSize[b];
    if (rank[a] == rank[b]) rank[a]++;
    return true;
  }

  int setSizeOf(const int &x) { return setSize[root(x)]; }

  int size() { return tree.size(); }
};

pair<Weight, Edges> kruskal(const Graph &g) {
  UnionFind uf(g.size());
  Edges es;
  for (auto &adj : g) {
    for (auto &e : adj) es.emplace_back(e);
  }
  sort(es.begin(), es.end(), [](const Edge &e, const Edge &f) { return e.weight < f.weight; });
  Weight total = 0;
  Edges tree;
  for (auto &e : es) {
    if (uf.unite(e.src, e.dst)) tree.push_back(e), total += e.weight;
  }
  return {total, tree};
}

main {
  while (true) {
    int n = in();
    if (n == 0) break;
    vector<double> x(n), y(n), z(n), r(n);
    rep(i, n) cin >> x[i] >> y[i] >> z[i] >> r[i];
    Graph g(n);
    rep(i, n) loop(j, i + 1, n) {
      double dx = abs(x[i] - x[j]), dy = abs(y[i] - y[j]), dz = abs(z[i] - z[j]);
      double d = max(0.0, sqrt(dx * dx + dy * dy + dz * dz) - r[i] - r[j]);
      g.addEdge(i, j, d);
    }
    cout << prec(3) << kruskal(g).first << endl;
  }
}



Measured memory_bytes: 3928