#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#include<ctime>

#include<cmath>

#include<cstdlib>

#define db double

#define ll long long

using namespace std;

const int N=;

const db dc=0.997,eps=1e-,INF=;

int n;

db nx[N],ny[N],nz[N],px,py,pz,ans;

db dis(db x0,db y0,db z0,db x1,db y1,db z1)

{

  return sqrt((x0-x1)*(x0-x1)+(y0-y1)*(y0-y1)+(z0-z1)*(z0-z1));

}

void SA(db T)

{

  db x=px,y=py,z=pz,pr=ans;int id;

  while(T>eps)

    {

      db d=;

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

    {

      db tmp=dis(x,y,z,nx[i],ny[i],nz[i]);

      if(tmp>d)d=tmp,id=i;

    }

      ans=min(ans,d);

      x=x+(nx[id]-x)/d*T;y=y+(ny[id]-y)/d*T;z=z+(nz[id]-z)/d*T;

      T*=dc;

    }

}

int main()

{

  srand(time());

  while()

    {

      scanf("%d",&n);if(!n)return ;

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

    scanf("%lf%lf%lf",&nx[i],&ny[i],&nz[i]),px+=nx[i],py+=ny[i],pz+=nz[i];

      px/=n;py/=n;pz/=n;

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

      ans=max(ans,dis(px,py,pz,nx[i],ny[i],nz[i]));

      SA();

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

    }

  return ;

}