#include <iostream>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <algorithm>
#include <math.h>
#include <string>
#include <climits>
#include <assert.h>
#include <iomanip>

#define FOR(i,a,b) for(int i= (a); i<((int)b); ++i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define IS_BIT_ON(bit, i) (bit & (1 << i))
#define BIT_ON(bit, i) (bit | (1 << i))
#define BIT_OFF(bit, i) (bit & ~(1 << i))
#define BIT_COUNT(bit) (__builtin_popcount(bit))

typedef long long LL;
template<typename T> std::vector<T> make_v(size_t a){return std::vector<T>(a);}
template<typename T,typename... Ts> auto make_v(size_t a, Ts... ts){ return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}    // C++14
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
void print() { std::cout << std::endl; }
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) { std::cout << head; if (sizeof...(tail) != 0) {std::cout << " ";} print(std::forward<Tail>(tail)...); }
template <class T> void print(std::vector<T> &v) {for (auto& a : v) { std::cout << a; if (&a != &v.back()) {std::cout << " ";} }std::cout << std::endl;}
template <class T> void print(std::vector<std::vector<T>> &vv) { for (auto& v : vv) { print(v); }}
inline bool inside(long long y, long long x, long long H, long long W) {return 0 <= y and y < H and 0 <= x and x < W; }
template<class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }
template<class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) { return abs(x1 - x2) + abs(y1 - y2); }
template<typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }

template<class T> inline std::vector<T> unique(std::vector<T> v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v;
}
// 初項s, 交差dのn個の数列の和
long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
    return n * (2 * s + (n - 1) * d) / 2;
}

// 2のべき乗数かどうか
bool is_power_of_two(long long x) {
    return !(x & (x - 1));
}

// aとbの最大公約数 O(log min(a, b))
long long gcd(long long a, long long b) {
    if (b == 0) { return a; }
    return gcd(b, a % b);
}

// 数列vの最大公約数 O(N log d)
long long gcd(std::vector<long long> &v) {
    long long ans = v[0];
    for (int i = 1; i < (int)v.size(); ++i) {
        ans = gcd(ans, v[i]);
    }
    return ans;
}

// aとbの最小公倍数 O(log min(a, b))
long long lcm(long long a, long long b) {
    long long g = gcd(a, b);
    return a / g * b;
}

const int INF = 1u << 30u;
const long long LINF = 1ull << 58u;
const double EPS = 1e-9;
const long double PI = acos(-1.0);
const std::vector<int> dy2 = {0, 1}, dx2 = {1, 0};  // 右，下
const std::vector<int> dy4 = {0, 1, 0, -1}, dx4 = {1, 0, -1, 0};    // 右，下，左，上
const std::vector<int> dy8 = { 0, -1, 0, 1, 1, -1, -1, 1 }, dx8 = { 1, 0, -1, 0, 1, 1, -1, -1 };

using namespace std;

struct Edge {
    int no;
    int from;
    int to;
    double cost;
    Edge() {}
    Edge(int from, int to, double cost) : from(from), to(to), cost(cost) {}
    Edge(int no, int from, int to, double cost) : no(no), from(from), to(to), cost(cost) {}
    bool operator<(const Edge& edge) const {
        return this->cost < edge.cost;
    }
    bool operator>(const Edge& edge) const {
        return this->cost > edge.cost;
    }
};

class UnionFind {
public:
    vector<int> parent;
    vector<int> setSize;

    UnionFind(unsigned int size) {
        parent.resize(size + 1);
        iota(parent.begin(), parent.end(), 0);
        setSize.resize(size + 1, 1);
    }

    // xとyが同じ集合に属するか
    bool isSameSet(int x, int y) {
        return findRoot(x) == findRoot(y);
    }

    // xとyの属する集合を併合
    void unionSet(int x, int y) {
        x = findRoot(x);
        y = findRoot(y);
        if (x == y) { return; }

        parent[x] = y;
        setSize[y] += setSize[x];
    }

private:
    // 木の根を求める
    int findRoot(int x) {
        if (parent[x] == x) {
            return x;
        }
        else {
            return parent[x] = findRoot(parent[x]);
        }
    }
};

/**
 * グラフの最小全域木を求める。O(|E| log|V|)
 * @param num_of_node ノード数
 * @param edges　エッジ　無向グラフならu -> vとv -> uの両方向入れる
 * @return
 */
double kruskal(int num_of_node, vector<Edge> &edges) {
    sort(edges.begin(), edges.end());

    UnionFind uf(num_of_node);
    double ans = 0;
    for (const auto e : edges) {
        if (!uf.isSameSet(e.from, e.to)) {
            uf.unionSet(e.from, e.to);
            ans += e.cost;
        }
    }

    return ans;
}


template<class T> class Distance {
public:
    static T euclidean_distance_2d(T x1, T y1, T x2, T y2) {
        return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    }

    static T euclidean_distance_3d(T x1, T y1, T z1, T x2, T y2, T z2) {
        return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) + (z1 - z2) * (z1 - z2));
    }
};


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    while (true) {
        LL N;
        cin >> N;

        if (N == 0) {
            return 0;
        }

        auto c = make_v<tuple<double, double, double, double>>(N);
        FOR(i, 0, N) {
            double X, Y, Z, R;
            cin >> X >> Y >> Z >> R;
            c[i] = make_tuple(X, Y, Z, R);
        }

        auto edges = make_v<Edge>(0);
        FOR(i, 0, N) {
            FOR(j, 0, N) {
                if (i == j) {
                    continue;
                }
                double X1, Y1, Z1, R1, X2, Y2, Z2, R2;
                tie(X1, Y1, Z1, R1) = c[i];
                tie(X2, Y2, Z2, R2) = c[j];

                double cost = Distance<double>::euclidean_distance_3d(X1, Y1, Z1, X2, Y2, Z2);
                cost -= (R1 + R2);
                edges.emplace_back(Edge(i, j, max(0.0, cost)));
            }
        }

        cout << fixed << setprecision(3) << kruskal(N, edges) << endl;
    }

    return 0;
}



Measured memory_bytes: 3616