#include <iostream>
#include <cmath>
#include <set>
#include <vector>

using namespace std;

struct Point {
   double x, y, z, r;
   Point(double x, double y, double z, double r) {
      this->x = x;
      this->y = y;
      this->z = z;
      this->r = r;
   }
   double distance(const Point& A) const {
      double ret = (sqrt((A.x - this->x) * (A.x - this->x) +
                         (A.y - this->y) * (A.y - this->y) +
                         (A.z - this->z) * (A.z - this->z))
                    - (A.r + this->r));
      if (ret < 0) { return 0; }
      else { return ret; }
   }
};

struct P {
   int index;
   double d;
   P(int index, double d) { this->index = index; this->d = d; }
   bool operator < (const P& p) const {
      return this->d < p.d;
   }
   bool operator == (const P& p) const {
      return fabsl(this->d - p.d) < 0.0001;
   }
};

int
main()
{
   int n;
   while (cin >> n && n) {
      vector<Point> input;
      for (int i = 0; i < n; i++) {
         double x, y, z, r;
         cin >> x >> y >> z >> r;
         input.push_back(Point(x, y, z, r));
      }
      int include[n];
      memset(include, 0, sizeof(include));
      multiset<P> Q;
      include[0] = true;
      for (int i = 0; i < n; i++) {
         if (include[i]) { continue; }
         Q.insert(P(i, input[i].distance(input[0])));
      }
      double ans = 0;
      while (!Q.empty()) {
         P p = *Q.begin();
         Q.erase(Q.begin());
         if (include[p.index]) { continue; }
         ans += p.d;
         include[p.index] = true;
         for (int i = 0; i < n; i++) {
            Q.insert(P(i, input[i].distance(input[p.index])));
         }
      }
      printf("%.03lf\n", ans);
   }
   return 0;
}