#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<cmath>

 #include<string>

 #include<algorithm>

 #include<queue>

 #include<vector>

 #include<map>

 using namespace std;

 struct Point{

     double x,y,z;

 }p[];

 double dist(Point a,Point b){

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

 }

 double ac(int n){

     double ans=1e9;

     Point tmp;

     tmp.x=tmp.y=tmp.z=;;

     int s=;

     double step=;

     double esp=0.0000001;

     while(step>esp){

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

             if(dist(tmp,p[s])<dist(tmp,p[i])) s=i;

         }

         double Dist=dist(tmp,p[s]);

         ans=min(ans,Dist);

         tmp.x+=(p[s].x-tmp.x)/Dist*step;

         tmp.y+=(p[s].y-tmp.y)/Dist*step;

         tmp.z+=(p[s].z-tmp.z)/Dist*step;

         step*=0.999;

     }

     return ans;

 }

 int main(){

     int n;

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

         if(!n) break;

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

             scanf("%lf %lf %lf",&p[i].x,&p[i].y,&p[i].z);

         }

         double ans=ac(n);

         printf("%.5f\n",ans);

     }

 }