#include "bits/stdc++.h"
#include<unordered_map>
#pragma warning(disable:4996)
using namespace std;

#include "bits/stdc++.h"
#include<unordered_map>
#pragma warning(disable:4996)
using namespace std;

struct Point3 {
	long double x;
	long double y;
	long double z;
	Point3() :x(0), y(0), z(0) {}
	Point3(const long double _x, const long double _y, const long double _z) :x(_x), y(_y), z(_z) {}
};

Point3 operator+(const Point3&l, const Point3& r) {
	return Point3(l.x + r.x, l.y + r.y, l.z + r.z);
}
Point3 operator+=(Point3&l, const Point3& r) {
	return l = Point3(l.x + r.x, l.y + r.y, l.z + r.z);
}
Point3 operator-(const Point3&l, const Point3& r) {
	return Point3(l.x - r.x, l.y - r.y, l.z - r.z);
}
Point3 operator-=(Point3&l, const Point3& r) {
	return l = Point3(l.x - r.x, l.y - r.y, l.z - r.z);
}
Point3 operator*(const Point3&l, const long double r) {
	return Point3(l.x * r, l.y * r, l.z * r);
}
Point3 operator*(const long double r, const Point3&l) {
	return l*r;
}
Point3 operator*=(Point3&l, const long double r) {
	return l = Point3(l.x * r, l.y * r, l.z * r);
}
Point3 operator/(const Point3&l, const long double r) {
	return Point3(l.x / r, l.y / r, l.z / r);
}
Point3 operator/=(Point3&l, const long double r) {
	return l = Point3(l.x / r, l.y / r, l.z / r);
}
const long double eps = 1e-9, pi = acos(-1.0);
const long double dtop = pi / 180.;
const long double ptod = 1. / dtop;

namespace std {
	bool operator<(const Point3 &lhs, const Point3 &rhs) {
		if (lhs.x< rhs.x - eps) return true;
		if (lhs.x > rhs.x + eps) return false;
		if (lhs.y< rhs.y - eps) return true;
		if (lhs.y > rhs.y + eps) return false;
		return lhs.z < rhs.z;
	}
}

// 点の入力
Point3 input_point() {
	long double x, y, z;
	cin >> x >> y >> z;
	return Point3(x, y, z);
}

// 誤差つき等号判定
bool eq(const long double a, const long double b) {
	return (abs(a - b) < eps);
}

// 内積
long double dot(const Point3& a, const Point3& b) {
	return a.x*b.x + a.y*b.y + a.z*b.z;
}

// 外積
Point3 cross(const Point3& a, const Point3& b) {
	return Point3(a.y*b.z - a.z*b.y, a.z*b.x - a.x*b.z, a.x*b.y - a.y*b.x);
}

//ノルム
long double norm(const Point3&p) {
	return (p.x*p.x + p.y*p.y + p.z*p.z);
}

long double abs(const Point3&p) {

	return sqrt(p.x*p.x + p.y*p.y + p.z*p.z);
}



//球
struct Sphere {
	Point3 p;
	long double r;
	Sphere() :p(), r(0) {}
	Sphere(const Point3 _point, const long double _radius) :p(_point), r(_radius) {}
};

// 直線の定義
class Line3 {
public:
	Point3 a, b;
	Line3() : a(Point3(0, 0, 0)), b(Point3(0, 0, 0)) {}
	Line3(Point3 a, Point3 b) : a(a), b(b) {}
	Point3 operator[](const int _num)const {
		if (_num == 0)return a;
		else if (_num == 1)return b;
		else assert(false);
	}
};

// 点の線分上判定
bool isis_sp(const Line3& s, const Point3& p) {
	return (abs(s.a - p) + abs(s.b - p) - abs(s.b - s.a) < eps);
}

// 垂線の足
Point3 proj(const Line3 &l, const Point3& p) {
	long double t = dot(p - l.a, l.a - l.b) / norm(l.a - l.b);
	return l.a + t * (l.a - l.b);
}
// 直線と点の距離
long double dist_lp3(const Line3& l, const Point3& p) {
	return abs(p - proj(l, p));
}
// 球と直線の交点
vector<Point3> is_lsp(const Sphere& c, const Line3& l) {
	vector<Point3> res;
	long double d = dist_lp3(l, c.p);
	if (d < c.r + eps) {
		long double len = (d > c.r) ? 0.0 : sqrt(c.r * c.r - d * d); //safety;
		Point3 nor = (l.a - l.b) / abs(l.a - l.b);
		res.push_back(proj(l, c.p) + len * nor);
		res.push_back(proj(l, c.p) - len * nor);
	}
	return res;
}
// 球と線分の交点
vector<Point3> is_ssp(const Sphere& c, const Line3& l) {
	vector<Point3> res(is_lsp(c, l));
	vector<Point3> nres;
	for (auto p : res) {
		if (isis_sp(l, p))nres.emplace_back(p);
	}
	return nres;
}


struct UnionFind {
	vector<int> data;
	UnionFind(int size) : data(size, -1) { }
	bool unionSet(int x, int y) {
		x = root(x); y = root(y);
		if (x != y) {
			if (data[y] < data[x]) swap(x, y);
			data[x] += data[y]; data[y] = x;
		}
		return x != y;
	}
	bool findSet(int x, int y) {
		return root(x) == root(y);
	}
	int root(int x) {
		return data[x] < 0 ? x : data[x] = root(data[x]);
	}
	int size(int x) {
		return -data[root(x)];
	}
};

int main() {
	while (1) {
		int n; cin >> n;
		if (!n)break;
		vector<Sphere>sps;
		for (int i = 0; i < n; ++i) {
			long double x, y, z, r; cin >>x>>y>>z>> r;
			sps.emplace_back(Point3(x, y, z), r);
		}
		vector<vector<long double>>diss(n, vector<long double>(n,0));
		for (int i = 0; i < n; ++i) {
			for (int j = 0; j < n; ++j) {
				if (i == j)diss[i][j] = 0;
				else {
					if (sps[i].r + sps[j].r > abs(sps[i].p - sps[j].p)) {
						bool flag = false;
						if (sps[i].r < sps[j].r) {
							flag = true;
							swap(sps[i].r, sps[j].r);
						}
						if (sps[i].r < abs(sps[i].p - sps[j].p) + sps[j].r) {

							diss[i][j] = 0;
						}
						else {
							//diss[i][j] = sps[i].r - (abs(sps[i].p - sps[j].p) + sps[j].r);
						}
						
						if (flag) {
							swap(sps[i].r, sps[j].r);
						}
					}
					else {
						diss[i][j] = abs(sps[i].p - sps[j].p) - sps[i].r - sps[j].r;
					}
				}
			}
		}
		priority_queue<pair<long double, int>, vector<pair<long double, int>>,greater<pair<long double,int>>>que;
		vector<bool>unit(n, false);
		que.push(make_pair(0,0));
		long double ans = 0;
		while (!que.empty()) {
			pair<long double, int>atop(que.top());
			que.pop();
			if (unit[atop.second])continue;
			else {
				unit[atop.second] = true;
				ans += atop.first;
				for (int i = 0; i < n; ++i) {
					if (!unit[i]) {
						que.push(make_pair(diss[atop.second][i],i));
					}
				}
			}
		}
		cout <<setprecision(3)<<fixed<< ans << endl;
	}
	return 0;
}

Measured memory_bytes: 3696