import java.io.*;
import java.util.*;
import java.text.*;

public class D_matsu {
	public static void main(String[] args)throws IOException{
		Scanner sc = new Scanner(System.in);
		DecimalFormat formatter = new DecimalFormat("#0.000");
		int n = sc.nextInt();
		while(n!=0){
			double data[][] = new double[n][4];
			for(int i=0;i<n;i++){
				data[i][0] = sc.nextDouble();
				data[i][1] = sc.nextDouble();
				data[i][2] = sc.nextDouble();
				data[i][3] = sc.nextDouble();
			}
			
			Solver s = new Solver(n,data);
			double ans = s.solve();
			
			System.out.println(formatter.format(ans));
			
			n = sc.nextInt();
		}
	}
}

class Solver{
	int size;
	int connected[];//expression of MF-SET
	PriorityQueue<Edge> q;
	Solver(int n,double data[][]){
		size = n;
		connected = new int[size];
		q = new PriorityQueue<Edge>();
		for(int i=0;i<n;i++){
			for(int j=i+1;j<n;j++){
				double elen = edgeLength(data[i],data[j]);
				Edge e = new Edge(i,j,elen);
				q.offer(e);
			}
		}
		for(int i=0;i<n;i++) connected[i] = i;
	}
	
	public double solve(){
		double corlen;
		corlen = 0;
		//Kruskal's algorithm
		while(!q.isEmpty()){
			Edge e = q.poll();
			int i = e.p1;
			int j = e.p2;
			if(connected[i]!=connected[j]){
				merge(i,j);
				corlen += e.length;
			}
		}
		return corlen;
	}
	
	//MERGE OF MF-SET
	private void merge(int i,int j){
		int m1 = connected[i];
		int m2 = connected[j];
		for(int k=0;k<size;k++){
			if(connected[k]==m2) connected[k] = m1;
		}
	}
	
	private double edgeLength(double d1[],double d2[]){
		double dx = d1[0]-d2[0];
		double dy = d1[1]-d2[1];
		double dz = d1[2]-d2[2];
		double dist = Math.sqrt(dx*dx+dy*dy+dz*dz);
		double prelen = dist - (d1[3]+d2[3]);
		if(prelen>=0.0) return prelen;
		else return 0.0;
	}
}

class Edge implements Comparable<Edge>{
	int p1;
	int p2;
	double length;
	Edge(int i,int j,double l){
		p1 = i;
		p2 = j;
		length = l;
	}
	public int compareTo(Edge e){
		if(length>e.length) return 1;
		else if(length==e.length) return 0;
		else return -1;
	}
}