#include<bits/stdc++.h>
using namespace std;
const int N=1005;
const double eps=1e-6;
int n,x[N],y[N],z[N];
double c[N][N],l[N][N],d[N];
bool v[N];

bool chk(double m){
	for(int i=1;i<=n;i++)d[i]=1e18,v[i]=0;
	d[1]=0;
	double s=0;
	for(int i=1;i<=n;i++){
		int u=-1;
		for(int j=1;j<=n;j++)if(!v[j]&&(u==-1||d[j]<d[u]))u=j;
		v[u]=1;s+=d[u];
		for(int j=1;j<=n;j++)if(!v[j])d[j]=min(d[j],c[u][j]-m*l[u][j]);
	}
	return s>=0;
}

int main(){
	//freopen("desertking.in","r",stdin);
	//freopen("desertking.out","w",stdout);
	while(scanf("%d",&n),n){
		for(int i=1;i<=n;i++)scanf("%d%d%d",&x[i],&y[i],&z[i]);
		for(int i=1;i<=n;i++)for(int j=i+1;j<=n;j++){
			c[i][j]=c[j][i]=fabs(z[i]-z[j]);
			l[i][j]=l[j][i]=hypot(x[i]-x[j],y[i]-y[j]);
		}
		double L=0,R=100;
		while(R-L>eps){
			double M=(L+R)/2;
			if(chk(M))L=M;
			else R=M;
		}
		printf("%.3f\n",L);
	}
}