/*
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*/
#include<iostream>
#include<stdio.h>
#include<math.h>
#include<stdlib.h>
using namespace std;
const int MAX=35;
const double INF=1e20;
const double eps=1e-6;
struct point
{
    double x,y,z;
}ps[MAX],q;
int n;

double dist(point a,point b)
{
    a.x-=b.x;
    a.y-=b.y;
    a.z-=b.z;
    return sqrt(a.x*a.x+a.y*a.y+a.z*a.z);
}

int maxD(point p)
{
    double res=0;
    int k=0;
    for(int i=0;i<n;++i)
    {
        double tmp=dist(p,ps[i]);
        if(tmp>res)
        {
            k=i;
            res=dist(p,ps[i]);
        }
    }
    return k;
}

int main()
{
    while(scanf("%d",&n),n)
    {
        for(int i=0;i<n;++i)
            scanf("%lf%lf%lf",&ps[i].x,&ps[i].y,&ps[i].z);
        double step=100;
        double ans=INF;
        q.x=q.y=q.z=0.0;
        int k=1;
        while(step>eps)
        {
                int d=maxD(q);
                   double tmp=dist(ps[d],q);
            if(tmp<ans)
                ans=tmp;
            double dx=ps[d].x-q.x;
            double dy=ps[d].y-q.y;
            double dz=ps[d].z-q.z;
            dx/=tmp;dy/=tmp;dz/=tmp;
            q.x=q.x+dx*step;
            q.y=q.y+dy*step;
            q.z=q.z+dz*step;
            step*=0.98;
        }
        printf("%.5f\n",ans+1e-7);
    }
    return 0;
}