#include<iostream>

#include<cmath>

#include<cstring>

#include<queue>

#include<vector>

#include<cstdio>

#include<algorithm>

#include<map>

#include<set>

#define rep(i,e) for(int i=0;i<(e);i++)

#define rep1(i,e) for(int i=1;i<=(e);i++)

#define repx(i,x,e) for(int i=(x);i<=(e);i++)

#define X first

#define Y second

#define PB push_back

#define MP make_pair

#define mset(var,val) memset(var,val,sizeof(var))

#define scd(a) scanf("%d",&a)

#define scdd(a,b) scanf("%d%d",&a,&b)

#define scddd(a,b,c) scanf("%d%d%d",&a,&b,&c)

#define pd(a) printf("%d\n",a)

#define scl(a) scanf("%lld",&a)

#define scll(a,b) scanf("%lld%lld",&a,&b)

#define sclll(a,b,c) scanf("%lld%lld%lld",&a,&b,&c)

#define IOS ios::sync_with_stdio(false);cin.tie(0)

#define lc idx<<1

#define rc idx<<1|1

#define rson mid+1,r,rc

#define lson l,mid,lc

using namespace std;

typedef long long ll;

template <class T>

void test(T a) {

    cout<<a<<endl;

}

template <class T,class T2>

void test(T a,T2 b) {

    cout<<a<<" "<<b<<endl;

}

template <class T,class T2,class T3>

void test(T a,T2 b,T3 c) {

    cout<<a<<" "<<b<<" "<<c<<endl;

}

const int inf = 0x3f3f3f3f;

const ll INF = 0x3f3f3f3f3f3f3f3fll;

const ll mod = 1e9+;

int T;

void testcase() {

    printf("Case %d: ",++T);

}

const int MAXN = 1e5+;

const int MAXM = ;

const double PI = acos(-1.0);

const double eps = 1e-;

struct node{

    double x,y,z,r;

}p[];

double dist(node a,node b){

    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z));

}

double g[][],lowc[];

bool vis[];

int main() {

#ifdef LOCAL

    freopen("data.in","r",stdin);

#endif // LOCAL

    int n;

    while(~scd(n)&&n){

        for(int i=;i<n;i++){

            scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&p[i].z,&p[i].r);

        }

        double maxx=0.0;

        for(int i=;i<n;i++){

            g[i][i]=0.0;

            for(int j=i+;j<n;j++){

                if(dist(p[i],p[j])-(p[i].r+p[j].r)<=eps){

                    g[i][j]=g[j][i]=0.0;

                }else{

                    g[i][j]=g[j][i]=dist(p[i],p[j])-(p[i].r+p[j].r);

                    maxx=max(maxx,g[i][j]);

                }

            }

        }

        mset(vis,false);

        double ans=;

        vis[]=true;

        for(int i=;i<n;i++) lowc[i]=g[][i];

        for(int i=;i<n;i++){

            double minc = maxx;

            int p=-;

            for(int j=;j<n;j++){

                if(!vis[j]&&minc>lowc[j]){

                    minc=lowc[j];

                    p=j;

                }

            }

            ans+=minc;

            vis[p]=true;

            for(int j=;j<n;j++){

                if(!vis[j]&&lowc[j]-g[p][j]>eps){

                    lowc[j]=g[p][j];

                }

            }

        }

        printf("%.3f\n",ans);

    }

    return ;

}