#include<iostream>

#include<cstdio>

#include<cmath>

#include<cstring>

#include<algorithm>

#include<vector>

#include<queue>

using namespace std;

const int maxn=1000;

int n;

double lenth[maxn],nowans,lef,righ,w[maxn][maxn],v[maxn][maxn];

bool intree[maxn];

double ab(double x)

{

 if(x>0)return x;

 	else return x*(-1);

}

class point

{

 public:

 double x;double y;double z;

};

point po[maxn];

double dist(point a,point b);

double cost(point a,point b)

{

 return ab((a.z-b.z));

}

class edge

{

 public:

 int  pa;int pb;

 double dis;double cos;double div;

 edge(int a,int b,double(*distance)(point,point),double (*cost)(point,point))

 {

  this->pa=a;this->pb=b;

  this->dis=distance(po[a],po[b]);

  this->cos=cost(po[a],po[b]);

  this->div=cos/dis;

 }

 bool operator <(const edge b)const

 {

  return (this->cos-(this->dis*nowans))>(b.cos-(b.dis*nowans));//这个算法的核心

 }

};

double dist(point a,point b)

{

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

}

double min(double a,double b)

{

 if(a<b)return a;

 	else return b;

}

int main()

{

 ios::sync_with_stdio(false);

 while(cin>>n)

 {

   if(n==0)return 0;

   lef=0.0;righ=1e6;

   for(int i=0;i<n;i++)

    	{

 	     cin>>po[i].x>>po[i].y>>po[i].z;

	    }

  for(int i=0;i<n;i++)

  	for(int j=0;j<n;j++)

  		{

  		 w[i][j]=cost(po[i],po[j]);

  		 v[i][j]=dist(po[i],po[j]);

		}

   double minnow;

  while(true)

   	{

   	 nowans=(lef+righ)/2;minnow=0;

   	 memset(intree,0,sizeof(intree));

   	 for(int i=1;i<n;i++)

   	 	{

   	 	 lenth[i]=w[0][i]-v[0][i]*nowans;

		}

   	 lenth[0]=0.0;intree[0]=true;

   	 for(int i=1;i<n;i++)

   	 	{

   	 	 double temp=1e+30;int tj=0;

   	 	 for(int j=1;j<n;j++)

   	 	 	if(!intree[j]&&lenth[j]<temp)

   	 	 		{

   	 	 		 tj=j;

   	 	 		 temp=lenth[j];

				}

		 minnow+=lenth[tj];

		 intree[tj]=true;

		 for(int j=1;j<n;j++)

		 	{

		 	 if(!intree[j])lenth[j]=min(lenth[j],w[tj][j]-v[tj][j]*nowans);

			}

		}

	 if(ab(minnow-0.0)<1e-5)break;

	 if(minnow>0)lef=nowans;

	 	else righ=nowans;

	}

  printf("%.3lf\n",(lef+righ)/2);

 }

 return 0;

}