#include <iostream>
#include <cstdio>
#include <vector>
#include <list>
#include <cmath>
#include <fstream>
#include <algorithm>
#include <string>
#include <queue>
#include <set>
#include <map>
#include <complex>
#include <iterator>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <stack>
#include <climits>
#include <deque>
#include <bitset>
#include <cassert>
#include <ctime>
using namespace std;

typedef long long ll;
typedef pair<int,int> pii;
const int dy[]={-1,0,1,0},dx[]={0,1,0,-1};
// adjust problem by problem
const double EPS=1e-8;
const double PI=acos(-1.0);
#define REP(i,n) for(int i=0;i<(int)n;++i)
#ifdef __GNUC__
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
int popcount(int n){return __builtin_popcount(n);}
int popcount(ll n){return __builtin_popcountll(n);}
#endif
#ifndef __GNUC__
template<class T> int popcount(T val){
  val = val - ((val >> 1) & 0x55555555);
  val = (val & 0x33333333) + ((val >> 2) & 0x33333333);
  val = (val + (val >> 4)) & 0x0f0f0f0f;
  val += val >> 8;
  val += val >> 16;
  return (int)(val & 0x0000003f);
}
#endif
template<class T>int SIZE(T a){return a.size();}
template<class T>string IntToString(T num){string res;stringstream ss;ss<<num;return ss.str();}
template<class T>T StringToInt(string str){T res=0;for(int i=0;i<SIZE(str);i++)res=(res*10+str[i]-'0');return res;}
template<class T>T gcd(T a,T b){if(b==0)return a;return gcd(b,a%b);}
template<class T>T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> void PrintSeq(T &a,int sz){for(int i=0;i<sz;i++){cout<<a[i];if(sz==i+1)cout<<endl;else cout<<' ';}}
ll getTen(int a){return (a<=0)?1:(getTen(a-1)*10);}
bool EQ(double a,double b){return abs(a-b)<EPS;}
void fastStream(){cin.tie(0);std::ios_base::sync_with_stdio(0);}
vector<string> split(string str,char del){
  vector<string> res;
  for(int i=0,s=0;i<SIZE(str);i++){
    if(str[i]==del){if(i-s!=0)res.push_back(str.substr(s,i-s));s=i+1;}
    else if(i==SIZE(str)-1){res.push_back(str.substr(s));}
  }
  return res;
}

int N;
double sy,sx,sz;
double gy,gx,gz;
double px[101][2];
double py[101][2];
double pz[101][2];
double d[101][101];

// 線分と点の間の距離を計算(3次元)
double calcDist(double x0,double y0,double z0,double x1,double y1,double z1,double px,double py,double pz){
  double res=0;
  double dy=y1-y0;
  double dz=z1-z0;
  double dx=x1-x0;
  double a=dx*dx+dy*dy+dz*dz;
  double b=dx*x0+dy*y0+dz*z0;
  double c=(dx*px+dy*py+dz*pz);
  double t=0;
  if(!EQ(a,0))t=(c-b)/a;
  double ox=x0+dx*t;
  double oy=y0+dy*t;
  double oz=z0+dz*t;
  res=sqrt((ox-px)*(ox-px)+(oy-py)*(oy-py)+(oz-pz)*(oz-pz));
  return res;
}


double calcDist(double x0,double y0,double z0,double x1,double y1,double z1
                ,double x2,double y2,double z2,double x3,double y3,double z3){
  double res=0;
  double a1=(x3-x2)*(x1-x0)+(y3-y2)*(y1-y0)+(z3-z2)*(z1-z0);
  double a2=(x1-x0)*(x1-x0)+(y1-y0)*(y1-y0)+(z1-z0)*(z1-z0);
  double a3=(x1-x0)*(x2-x0)+(y1-y0)*(y2-y0)+(z1-z0)*(z2-z0);
  double b1=(x3-x2)*(x3-x2)+(y3-y2)*(y3-y2)+(z3-z2)*(z3-z2);
  double b2=(x1-x0)*(x3-x2)+(y1-y0)*(y3-y2)+(z1-z0)*(z3-z2);
  double b3=(x3-x2)*(x2-x0)+(y3-y2)*(y2-y0)+(z3-z2)*(z2-z0);
  double t,s;
  // cout<<a1<<" "<<a2<<" "<<a3<<" ";
  // cout<<b1<<" "<<b2<<" "<<b3<<endl;
  if(a1==0){
    t=a3/a2;
    s=(t*b2-b3)/b1;
  }
  else if(a2==0){
    s=-a3/a1;
    t=(s*b1+b3)/b2;
  }
  else if(b1==0){
    t=b3/b2;
    s=(t*a2-a3)/a1;
  }
  else if(b2==0){
    s=-b3/b1;
    t=(s*a1+a3)/a2;
  }
  else{
    if(a2*b1-a1*b2==0)t=0;
    else t=(a3*b1-a1*b3)/(a2*b1-a1*b2);
    s=(t*a2-a3)/a1;
  }
  
  double p1x=x0+t*(x1-x0);
  double p1y=y0+t*(y1-y0);
  double p1z=z0+t*(z1-z0);

  double p2x=x2+s*(x3-x2);
  double p2y=y2+s*(y3-y2);
  double p2z=z2+s*(z3-z2);

  res=sqrt((p1x-p2x)*(p1x-p2x)+(p1y-p2y)*(p1y-p2y)+(p1z-p2z)*(p1z-p2z));
  
  return res;
}

struct Point{
  double x,y,z;
  Point(double x_,double y_,double z_){
    x=x_;
    y=y_;
    z=z_;
  }
  Point(){}
};

Point cross(Point p1,Point p2){
  return Point(p1.y*p2.z-p1.z*p2.y,p1.z*p2.x-p1.x*p2.z,p1.x*p2.y-p1.y*p2.x);
}
double dot(Point p1,Point p2){
  return p1.x*p2.x+p1.y*p2.y+p1.z*p2.z;
}
double abs(Point p){
  return sqrt(p.x*p.x+p.y*p.y+p.z*p.z);
}

/*
  線分間距離ではなく、直線間距離を計算
 */

int main(){

  while(cin>>N&&N){
    cin>>sx>>sy>>sz>>gx>>gy>>gz;
    for(int i=0;i<N;i++)
      for(int j=0;j<2;j++)
        cin>>px[i][j]>>py[i][j]>>pz[i][j];
    // すべての線分間の距離を計算
    for(int i=0;i<N;i++){
      for(int j=i;j<N;j++){
        if(i==j)d[i][j]=0;
        else{
          d[j][i]=d[i][j]=calcDist(px[i][0],py[i][0],pz[i][0],px[i][1],py[i][1],pz[i][1]
                           ,px[j][0],py[j][0],pz[j][0],px[j][1],py[j][1],pz[j][1]);
        }
      }
    }
    for(int k=0;k<N;k++)
      for(int i=0;i<N;i++)
        for(int j=0;j<N;j++)
          d[i][j]=min(d[i][j],d[i][k]+d[k][j]);
    //double res=1e+15;
    // // sy,sx,szとgx,gy,gzの２点がどのノード上に乗っているか調べる
    // for(int i=0;i<N;i++){
    //   for(int j=0;j<N;j++){
    //     double dist=calcDist(px[i][0],py[i][0],pz[i][0],px[i][1],py[i][1],pz[i][1],sx,sy,sz);
    //     //cout<<i<<" "<<j<<" "<<dist<<endl;
    //     dist+=calcDist(px[j][0],py[j][0],pz[j][0],px[j][1],py[j][1],pz[j][1],gx,gy,gz);
    //     dist+=d[i][j];
    //     res=min(res,dist);
    //   }
    // }
    //printf("%.10f\n",res);
    int spos=-1,gpos=-1;
    for(int i=0;i<N;i++){
      if(EQ(0,calcDist(px[i][0],py[i][0],pz[i][0],px[i][1],py[i][1],pz[i][1],sx,sy,sz)))spos=i;
      if(EQ(0,calcDist(px[i][0],py[i][0],pz[i][0],px[i][1],py[i][1],pz[i][1],gx,gy,gz)))gpos=i;
    }
    //cout<<spos<<" "<<gpos<<endl;
    printf("%.10f\n",d[spos][gpos]);
  }
  
  
  return 0;
}

Measured memory_bytes: 1336