#include <cstdio>

 #include <cstring>

 #include <queue>

 #include <cmath>

 #include <algorithm>

 #include <set>

 #include <iostream>

 #include <map>

 #include <stack>

 #include <string>

 #include <vector>

 #define  pi acos(-1.0)

 #define  eps 1e-8

 #define  fi first

 #define  se second

 #define  rtl   rt<<1

 #define  rtr   rt<<1|1

 #define  bug         printf("******\n")

 #define  mem(a,b)    memset(a,b,sizeof(a))

 #define  name2str(x) #x

 #define  fuck(x)     cout<<#x" = "<<x<<endl

 #define  f(a)        a*a

 #define  sf(n)       scanf("%d", &n)

 #define  sff(a,b)    scanf("%d %d", &a, &b)

 #define  sfff(a,b,c) scanf("%d %d %d", &a, &b, &c)

 #define  sffff(a,b,c,d) scanf("%d %d %d %d", &a, &b, &c, &d)

 #define  pf          printf

 #define  FRE(i,a,b)  for(i = a; i <= b; i++)

 #define  FREE(i,a,b) for(i = a; i >= b; i--)

 #define  FRL(i,a,b)  for(i = a; i < b; i++)+

 #define  FRLL(i,a,b) for(i = a; i > b; i--)

 #define  FIN         freopen("data.txt","r",stdin)

 #define  gcd(a,b)    __gcd(a,b)

 #define  lowbit(x)   x&-x

 using namespace std;

 typedef long long  LL;

 typedef unsigned long long ULL;

 const int mod = 1e9 + ;

 const int maxn = 2e5 + ;

 const int INF = 0x3f3f3f3f;

 const LL INFLL = 0x3f3f3f3f3f3f3f3fLL;

 int n;

 struct node {

     double p[];

 } qu[maxn];

 double cal ( node a ) {

     double cnt = ;

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

         cnt = max ( cnt, sqrt ( ( a.p[] - qu[i].p[] ) * ( a.p[] - qu[i].p[] ) + ( a.p[] - qu[i].p[] ) * ( a.p[] - qu[i].p[] ) + ( a.p[] - qu[i].p[] ) * ( a.p[] - qu[i].p[] ) ) );

     return cnt;

 }

 node check ( int cnt, node now ) {

     if ( cnt >=  ) return  now;

     node ans1, ans2, ans, temp1, temp2;

     double l = -, r = , ll, rr;

     ans = temp1 = temp2 = now;

     while ( eps < r - l ) {

         ll = (  * l + r ) / , rr = (  * r + l ) / ;

         temp1.p[cnt] = ll, temp2.p[cnt] = rr;

         ans1 = check ( cnt + , temp1 );

         ans2 = check ( cnt + , temp2 );

         if ( cal ( ans1 ) > cal ( ans2 ) ) ans = ans1, l = ll;

         else r = rr, ans = ans2;

     }

     return ans;

 }

 int main()  {

     while ( ~sf ( n ) ) {

         for ( int i =  ; i < n ; i++ ) scanf ( "%lf%lf%lf", &qu[i].p[], &qu[i].p[], &qu[i].p[] );

         node ans;

         printf ( "%lf\n", cal ( check ( , ans ) ) );

     }

     return ;

 }