#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <numeric>
#include <queue>
#include <stack>
#include <map> 
#include <set>
#include <string>
#include <functional>
#include <list>
#include <random>
#include <time.h>
#include <iomanip>
#include <assert.h>
#include <numeric>
#include <new>
#include <sstream>
#include <complex>
#define BIT(nr) (1ULL << (nr))
#define int long long
#define ll long long
#define double long double
#define mod 1000000007
#define MAXN (int)1e+5 * 2+1
#define LL_MAX 9223372036854775807	
#define LL_HALFMAX 9223372036854775807 / 2	
#define MIN -(9223372036854775807 / 2)
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
#define REPS(i,x) for(int i=1;i<=(int)(x);i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RREPS(i,x) for(int i=((int)(x));i>0;i--)
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define mp make_pair
template<typename T1, typename T2> inline void chmin(T1& a, T2 b) { if (a > b) a = b; }
template<typename T1, typename T2> inline void chmax(T1& a, T2 b) { if (a < b) a = b; }

using namespace std;

using Weight = double;
using Flow = int;
struct Edge {
	int src, dst;

	// libalgo のものに追加、メンバを追加するだけなので互換性は崩さないはず、逆辺のG[e.dstの]インデックスを保持
	int rev;
	Weight weight;
	Flow cap;
	Edge() : src(0), dst(0), weight(0) {}
	Edge(int s, int d, Weight w) : src(s), dst(d), weight(w) {}
	bool operator<(const Edge& right) const {
		return dst < right.dst;
	}
};

using Edges = std::vector<Edge>;
using Graph = std::vector<Edges>;
using Array = std::vector<Weight>;
using Matrix = std::vector<Array>;

void add_edge(Graph& g, int a, int b, Weight w = 1) {
	g[a].emplace_back(a, b, w);
	g[b].emplace_back(b, a, w);
}
void add_arc(Graph& g, int a, int b, Weight w = 1) { g[a].emplace_back(a, b, w); }

int dx[4] = { 0, 1, 0, -1 }; // x軸方向への変位
int dy[4] = { 1, 0, -1, 0 }; // y軸方向への変位

struct uf_tree {
	std::vector<int> parent;
	int __size;
	uf_tree(int size_) : parent(size_, -1), __size(size_) {}
	void unite(int x, int y) {
		if ((x = find(x)) != (y = find(y))) {
			if (parent[y] < parent[x]) std::swap(x, y);
			parent[x] += parent[y];
			parent[y] = x;
			__size--;
		}
	}
	bool is_same(int x, int y) { return find(x) == find(y); }
	int find(int x) { return parent[x] < 0 ? x : parent[x] = find(parent[x]); }
	int size(int x) { return -parent[find(x)]; }
	int size() { return __size; }
};

class Vector3D {
public:
	double x, y, z;
	Vector3D(double x, double y, double z) {
		this->x = x;
		this->y = y;
		this->z = z;
	}

	Vector3D operator- (Vector3D right) {
		return Vector3D(right.x - x, right.y - y, right.z - z);
	}

	double Length() {
		return sqrtl(x * x + y * y + z * z);
	}
};

bool solve() {
	int n;
	cin >> n;
	if (n == 0) {
		return false;
	}

	vector<Vector3D> points;
	vector<double> r;
	rep(i, n) {
		double x, y, z, ri;
		cin >> x >> y >> z >> ri;

		points.emplace_back(x, y, z);
		r.push_back(ri);
	}

	auto cmp = [](const Edge& l, const Edge& r) {
		return l.weight < r.weight;
	};

	vector<Edge> es;

	rep(i, n) {
		REP(j, i + 1, n) {
			double cand = (points[j] - points[i]).Length() - (r[i] + r[j]);
			double cost = max(0.0L, cand);
			es.emplace_back(i, j, cost);
		}
	}

	// MST
	double ans = 0;

	uf_tree uf(n);
	sort(ALLOF(es), cmp);

	for (auto e : es) {
		if (!uf.is_same(e.src, e.dst)) {
			uf.unite(e.src, e.dst);
			ans += e.weight;
		}
	}

	cout << fixed << setprecision(3) << ans << "\n";

	return true;
}

signed main() {
	while(solve()){}

	return 0;
}


Measured memory_bytes: 3736