#include "bits/stdc++.h"
#define Rep(i,n) for(int i=0;i<(int)(n);i++)
#define For(i,n1,n2) for(int i=(int)(n1);i<(int)(n2);i++)
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define RREP(i,n) for(ll i=((ll)(n)-1);i>=0;i--)
#define FOR(i,n1,n2) for(ll i=(ll)(n1);i<(ll)(n2);i++)
#define RFOR(i,n1,n2) for(ll i=((ll)(n1)-1);i>=(ll)(n2);i--)
#define all(a)  (a).begin(),(a).end()
#define IOS std::cin.tie(0),std::ios::sync_with_stdio(false)

namespace idaten {

	using namespace std;
	using ll = int_fast64_t;
	using ull = uint_fast64_t;
	using P = std::pair<int64_t, int64_t>;
	template<typename T1, typename T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return 1; }return 0; }
	template<typename T1, typename T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return 1; }return 0; }
	template<class T> inline std::istream& operator >> (std::istream& is, std::vector<T>& v) { for (T& x : v) { is >> x; }return is; }
	template<class T> inline std::ostream& operator << (std::ostream& os, const std::vector<T>& v) {
		for (auto itr = v.begin(); itr != v.end();) { os << (*itr) << ((++itr != v.end()) ? " " : ""); }
		return os;
	}
	template<class V, typename T>inline void fill(V& v, const T& val) { v = val; }
	template<class V, typename T>inline void fill(std::vector<V>& v, const T& val) { for (V& x : v) { fill(x, val); } }
	template<class V, typename H>inline void resize(std::vector<V>& v, const H h) { v.resize(h); }
	template<class V, typename H, typename... T>inline void resize(std::vector<V>& v, const H& h, const T& ... t) { v.resize(h); for (auto& x : v) { resize(x, t...); } }
	inline void put() {}
	template<class T> inline void put(const T& first) { std::cout << first << "\n"; }
	template<class T, class... N> inline void put(const T& first, const N& ... rest) { std::cout << first << " "; put(rest...); }

	class UnionFind {
	private:
		vector<int> par, height, size;
	public:
		UnionFind(int n) {
			par.resize(n);
			for (int i = 0; i < n; ++i) {
				par[i] = i;
			}
			height.resize(n, 0);
			size.resize(n, 1);
		}
		int root(int x) {
			if (par[x] == x) {
				return x;
			} else {
				par[x] = root(par[x]);
				return par[x];
			}
		}
		bool same(int x, int y) {
			return root(x) == root(y);
		}
		void unite(int x, int y) {
			x = root(x);
			y = root(y);
			if (x == y)return;
			if (height[x] < height[y]) {
				par[x] = y;
				size[y] += size[x];
			} else {
				par[y] = x;
				size[x] += size[y];
				if (height[x] == height[y])height[x]++;
			}
		}
		int cnt(int x) {
			x = root(x);
			return size[x];
		}
	};

	template<typename T>
	class MinimumSpanningTree {
	private:
		vector<int> from, to;
		vector<pair<T, int>> cost;
		int n, m;
	public:
		MinimumSpanningTree<T>(vector<int>& from, vector<int>& to, vector<T>& cost, int n) : from(from), to(to), n(n) {
			this->m = (int)cost.size();
			this->cost.resize(m);
			for (int i = 0; i < m; ++i) {
				this->cost[i].first = cost[i];
				this->cost[i].second = i;
			}
			sort(this->cost.begin(), this->cost.end());
		}
		vector<int> Kruskal() {
			vector<int> res; //mstを構成するindexの集合
			UnionFind uf(this->n);
			for (int i = 0; i < this->m; ++i) {
				int index = this->cost[i].second;
				if (!uf.same(this->from[index], this->to[index])) {
					res.push_back(index);
					uf.unite(this->from[index], this->to[index]);
				}
				if (res.size() == n - 1) {
					break;
				}
			}
			return res;
		}
	};


	void solve() {
		IOS;
		int n;
		cin >> n;
		cout << fixed << setprecision(3);
		while (n) {
			vector<double> x(n), y(n), z(n), r(n);
			REP(i, n) {
				cin >> x[i] >> y[i] >> z[i] >> r[i];
			}
			vector<int> from, to;
			vector<double> cost;
			REP(i, n) {
				FOR(j, i + 1, n) {
					double dx = (x[i] - x[j]);
					double dy = (y[i] - y[j]);
					double dz = (z[i] - z[j]);
					double c = sqrt(dx * dx + dy * dy + dz * dz);
					c = max(0.0, c - r[i] - r[j]);
					from.push_back(i);
					to.push_back(j);
					cost.push_back(c);
					//to.push_back(i);
					//from.push_back(j);
					//cost.push_back(c);
				}
			}
			MinimumSpanningTree<double> mst(from, to, cost, n);
			auto krs = mst.Kruskal();
			double res = 0;
			for (auto&& v : krs) {
				res += cost[v];
			}
			put(res);
			cin >> n;
		}
		
	}
} // namespace idaten

int main() {
	idaten::solve();
	return 0;
}



Measured memory_bytes: 3328