1 #include<bits/stdc++.h>

 2 using namespace std;

 3 const int M=1006;

 4 const double eps=1e-8;

 5 struct node{

 6     double x,y,z;

 7 }p[M];

 8 double a[M][M],c[M][M];

 9 bool v[M];

10 double d[M];

11 int n;

12

13 double dist(int i,int j){

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

15 }

16

17 bool ck(double b){

18     double ans=0;

19     for(int i=0;i<=n+1;i++) d[i]=1e18;

20     memset(v,0,sizeof(v));

21     d[1]=0;

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

23         int x=0;

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

25             if(!v[j]&&(x==0||d[j]<d[x])) x=j;

26         v[x]=1;

27         ans+=d[x];

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

29             if(!v[j]) d[j]=min(d[j],c[x][j]-b*a[x][j]);

30     }

31     if(ans+eps>=0) return true;

32     return false;

33 }

34

35 int main(){

36     while(cin>>n&&n){

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

38             double x,y,z;

39             cin>>x>>y>>z;

40             p[i]=(node){x,y,z};

41         }

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

43             for(int j=i+1;j<=n;j++){

44                 a[i][j]=a[j][i]=dist(i,j);

45                 c[i][j]=c[j][i]=abs(p[i].z-p[j].z);

46             }

47         double l=0,r=1e8;

48         while(l+eps<r){

49             double mid=(l+r)/2.0;

50             if(ck(mid)) l=mid;

51             else r=mid;

52         }

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

54     }

55     return 0;

56 }