#include<iostream>

 #include<cmath>

 #include<iomanip>

 #include<string.h>

 const int N=;

 const int inf=0x7fffffff;

 using namespace std;

 int n,book[N];

 double x[N],y[N],h[N],w2[N][N],w1[N][N],ans,dis[N];

 double prim(double mid){

     double mn;

     ans=;

     memset(book,,sizeof(book));

     int now;

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

         dis[i]=w2[][i]-w1[][i]*mid;

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

         mn=inf;

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

             if(!book[j]&&mn>dis[j]){

                 now=j;

                 mn=dis[j];

             }

         book[now]=;

         ans+=mn;

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

             if(!book[j]&&dis[j]>w2[now][j]-w1[now][j]*mid)

                 dis[j]=w2[now][j]-w1[now][j]*mid;

     }

     return ans;

 }

 double kf(int i,int j){

     return sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));

 }

 int main(){

     while(scanf("%d",&n)&&n){

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

             scanf("%lf%lf%lf",&x[i],&y[i],&h[i]);

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

                 w1[i][j]=w1[j][i]=kf(i,j);

                 w2[i][j]=w2[j][i]=abs(h[i]-h[j]);

             }

         }

         double l=0.0,r=1000.0,mid;

         while(r-l>1e-){

             mid=(l+r)/;

             if(prim(mid)>=) l=mid;

             else r=mid;

         }

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

     }

 }