/************************************************
* Author        :Running_Time
* Created Time  :2015/10/25 12:00:48
* File Name     :POJ_2031.cpp************************************************/#include <cstdio>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <cstring>
#include <cmath>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <bitset>
#include <cstdlib>
#include <ctime>
using namespace std;#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
typedef long long ll;
const int N = 1e2 + 10;
const int E = N * N;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
const double EPS = 1e-10;bool vis[N];
double d[N];
int head[N];
int n, m, e;
int dcmp(double x)  {       //三态函数，减少精度问题 if (fabs (x) < EPS) return 0; else    return x < 0 ? -1 : 1;
}
struct Point    {double x, y, z, a;Point () {}Point (double x, double y, double z, double a) : x (x), y (y), z (z), a (a) {}Point operator - (const Point &r) const {       //向量减法 return Point (x - r.x, y - r.y, z - r.z, 0); }
};
typedef Point Vector;       //向量的定义
Point read_point(void)   {      //点的读入 double x, y, z, r; scanf ("%lf%lf%lf%lf", &x, &y, &z, &r); return Point (x, y, z, r);
}
double dot(Vector A, Vector B)  {       //向量点积 return A.x * B.x + A.y * B.y + A.z * B.z;
}
double length(Vector A) {       //向量长度，点积 return sqrt (dot (A, A));
} struct Edge {int v, nex;double w;Edge () {}Edge (int v, double w, int nex) : v (v), w (w), nex (nex) {}bool operator < (const Edge &r) const   {return w > r.w;}
}edge[E];void init(void) {memset (head, -1, sizeof (head));e = 0;
}void add_edge(int u, int v, double w)   {edge[e] = Edge (v, w, head[u]);head[u] = e++;
}double Prim(int s) {memset (vis, false, sizeof (vis));for (int i=0; i<n; ++i) d[i] = 1e9;priority_queue<Edge> Q;for (int i=head[s]; ~i; i=edge[i].nex)  {int v = edge[i].v;  double w = edge[i].w;if (d[v] > w)   {d[v] = w;   Q.push (Edge (v, d[v], 0));}}vis[s] = true;  d[s] = 0;double ret = 0;while (!Q.empty ()) {int u = Q.top ().v; Q.pop ();if (vis[u]) continue;vis[u] = true;  ret += d[u];for (int i=head[u]; ~i; i=edge[i].nex)  {int v = edge[i].v;  double w = edge[i].w;if (!vis[v] && d[v] > w)   {d[v] = w;    Q.push (Edge (v, d[v], 0));}}}return ret;
}Point p[N];
int main(void)    {while (scanf ("%d", &n) == 1)   {if (!n) break;for (int i=0; i<n; ++i) {p[i] = read_point ();}init ();for (int i=0; i<n; ++i) {for (int j=i+1; j<n; ++j)   {double dis = length (p[i] - p[j]);double len = p[i].a + p[j].a;if (dcmp (dis - len) <= 0)   {add_edge (i, j, 0);add_edge (j, i, 0);}else    {add_edge (i, j, dis - len);add_edge (j, i, dis - len);}}}printf ("%.3f\n", Prim (0));}return 0;
}