#include<cstdio>

#include<cmath>

#include<algorithm>

#include<cstdlib>

using namespace std;

const double EPS=0.00000001;

const double PI=acos(-1.0);

struct Point{

	double x,y,z;

	Point(const double &x,const double &y,const double &z){

		this->x=x;

		this->y=y;

		this->z=z;

	}

	Point(){}

	void read(){

		scanf("%lf%lf%lf",&x,&y,&z);

	}

	double length(){

		return sqrt(x*x+y*y+z*z);

	}

}a[35],p,allp;

double ans,allans;

int n;

typedef Point Vector;

Vector operator - (const Point &a,const Point &b){

	return Vector(a.x-b.x,a.y-b.y,a.z-b.z);

}

Vector operator + (const Vector &a,const Vector &b){

	return Vector(a.x+b.x,a.y+b.y,a.z+b.z);

}

Vector operator * (const double &K,const Vector &v){

	return Vector(K*v.x,K*v.y,K*v.z);

}

double calc(Point p){

	double res=0.0;

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

		res=max(res,(a[i]-p).length());

	}

	return res;

}

//double ran(){

//	int fm=rand()%10000+1;

//	return ((rand()&1) ? -1.0 : 1.0)*((double)(rand()%(fm+1))/(double)fm);

//}

Vector unit(Vector v){

	double l=v.length();

	return Vector(v.x/l,v.y/l,v.z/l);

}

int main(){

	srand(233);

	//freopen("poj2069.in","r",stdin);

	while(1){

		scanf("%d",&n);

		if(!n){

			return 0;

		}

		allans=100000.0;

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

			a[i].read();

		}

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

			p=a[1];

			ans=calc(p);

			double T=sqrt(20000.0);

			while(T>EPS){

				double bestnow=100000.0;

				Point besttp;

//				for(int i=1;i<=30;++i){

//					double rad=(double)(rand()%10000+1)/10000.0*2.0*PI;

					int to;

					double far=0.0;

					for(int k=1;k<=n;++k){

						double tmp=(a[k]-p).length();

						if(tmp>far){

							far=tmp;

							to=k;

						}

					}

					Point tp=p+T*unit(a[to]-p);

					double now=calc(tp);

					if(now<bestnow){

						bestnow=now;

						besttp=tp;

					}

//				}

				if(bestnow-100000.0<-EPS && (bestnow<ans || exp((ans-bestnow)/T)*10000.0>(double)(rand()%10000))){

					ans=bestnow;

					p=besttp;

				}

				T*=0.99;

			}

			if(ans<allans){

				allans=ans;

//				allp=p;

			}

//		}

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

	}

	return 0;

}