#include<cstdio>

#include<algorithm>

#include<cstring>

#include<cmath>

#define N 1005

using namespace std;

int n,tot;

double x[N],y[N],z[N],dis[N];

bool vis[N];

double mul(double x) {return x*x;}

double dist(int a,int b)

{

    return sqrt(mul(x[a]-x[b])+mul(y[a]-y[b]));

}

bool check(double mid)

{

    memset(vis,,sizeof(vis));

    for (int i=;i<=n;i++) dis[i]=fabs(z[]-z[i])-mid*dist(,i);

    vis[]=;

    int tot=n-;

    int id=-;

    double val=0.0,tmp=0.0;

    while(tot--)

    {

    id=-;

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

    {

        if(!vis[i])

        {

        if(id==-) id=i;

        else if(dis[id]>dis[i]) id=i;

        }

    }

    tmp+=dis[id];

    vis[id]=;

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

    {

        if(!vis[i])

        {

        dis[i]=min(dis[i],fabs(z[i]-z[id])-mid*dist(i,id));

        }

    }

    }

    return tmp<=0.0;

}

int main()

{

    while (scanf("%d",&n)!=EOF)

    {

    if (!n) break;

    for (int i=;i<=n;i++) scanf("%lf%lf%lf",&x[i],&y[i],&z[i]);

    double l=0.0,r=0.0,mid;

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

        r+=fabs(z[i]-z[]);

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

    {

        mid=(l+r)/2.0;

        if (check(mid)) r=mid;

        else l=mid;

    }

    printf("%.3lf\n",r);

    }

    return ;

}