#include<bits/stdc++.h>

#define REP(i,s,n) for(int i=s;i<n;i++)
#define rep(i,n) REP(i,0,n)
#define EPS (1e-8)
#define COUNTER_CLOCKWISE 1
#define CLOCKWISE -1 
#define ONLINE_BACK 2
#define ONLINE_FRONT -2
#define ON_SEGMENT 0
#define equals(a,b) (fabs((a)-(b)) < EPS)

using namespace std;

const int IINF = INT_MAX;

class Point{
public:
  double x,y;
  Point(double x = 0,double y = 0): x(x),y(y){}
  Point operator + (Point p){return Point(x+p.x,y+p.y);}
  Point operator - (Point p){return Point(x-p.x,y-p.y);}
  Point operator * (double a){return Point(a*x,a*y);}
  Point operator / (double a){return Point(x/a,y/a);}
  bool operator < (const Point& p) const{ return !equals(x,p.x)?x<p.x:y<p.y; }
  bool operator == (const Point& p)const{ return fabs(x-p.x) < EPS && fabs(y-p.y) < EPS; }

};

struct Segment{
  Point p1,p2;
  Segment(Point p1 = Point(),Point p2 = Point()):p1(p1),p2(p2){}
  bool operator == (const Segment& p)const { return ( p.p1 == p1 && p.p2 == p2 ) || ( p.p1 == p2 && p.p2 == p1 ); }
  bool operator < (const Segment& s) const {
    if( !( p1 == s.p1 ) ) return p1 < s.p1;
    return p2 < s.p2;
  }
};

typedef Point Vector;
typedef Segment Line;
typedef vector<Point> Polygon;

double dot(Point a,Point b){ return a.x*b.x + a.y*b.y; }
double cross(Point a,Point b){ return a.x*b.y - a.y*b.x; }
double norm(Point a){ return a.x*a.x+a.y*a.y; }
double abs(Point a){ return sqrt(norm(a)); }

int ccw(Point p0,Point p1,Point p2){
  Point a = p1-p0;
  Point b = p2-p0;
  if(cross(a,b) > EPS)return COUNTER_CLOCKWISE;
  if(cross(a,b) < -EPS)return CLOCKWISE;
  if(dot(a,b) < -EPS)return ONLINE_BACK;
  if(norm(a) < norm(b))return ONLINE_FRONT;
  return ON_SEGMENT;
}

bool intersectLS(Line l, Line s) {
  return cross(l.p2-l.p1, s.p1-l.p1)*       // s[0] is left of l
    cross(l.p2-l.p1, s.p2-l.p1) < EPS; // s[1] is right of l
}

bool intersectSS(Line s, Line t) {
  return ccw(s.p1,s.p2,t.p1)*ccw(s.p1,s.p2,t.p2) <= 0 &&
    ccw(t.p1,t.p2,s.p1)*ccw(t.p1,t.p2,s.p2) <= 0;
}

Point projection(Line l,Point p) {
  double t = dot(p-l.p1, l.p1-l.p2) / norm(l.p1-l.p2);
  return l.p1 + (l.p1-l.p2)*t;
}
Point reflection(Line l,Point p) {
  return p + (projection(l, p) - p) * 2;
}

Point crosspoint(Line l,Line m){
  double A = cross(l.p2-l.p1,m.p2-m.p1);
  double B = cross(l.p2-l.p1,l.p2-m.p1);
  if(abs(A) < EPS && abs(B) < EPS){
    vector<Point> vec;
    vec.push_back(l.p1),vec.push_back(l.p2),vec.push_back(m.p1),vec.push_back(m.p2);
    sort(vec.begin(),vec.end());
    assert(vec[1] == vec[2]); //同じセグメントかもよ
    return vec[1];
  }
  return m.p1 + (m.p2-m.p1)*(B/A);
}

double cross3p(Point p,Point q,Point r){ return (r.x-q.x) * (p.y -q.y) - (r.y - q.y) * (p.x - q.x); }
bool collinear(Point p,Point q,Point r){ return fabs(cross3p(p,q,r)) < EPS; }
bool ccwtest(Point p,Point q,Point r){ return cross3p(p,q,r) > 0; }
bool onSegment(Point p,Point q,Point r){
  return collinear(p,q,r) && equals(sqrt(pow(p.x-r.x,2)+pow(p.y-r.y,2)) + sqrt(pow(r.x-q.x,2) + pow(r.y-q.y,2) ),sqrt(pow(p.x-q.x,2)+pow(p.y-q.y,2)) ) ;
}

double angle(Point a,Point b,Point c){
  double ux = b.x - a.x, uy = b.y - a.y;
  double vx = c.x - a.x, vy = c.y - a.y;
  return acos((ux*vx + uy*vy)/sqrt((ux*ux + uy*uy) * (vx*vx + vy*vy)));
}  
  
bool inPolygon(Polygon poly,Point p){
  if((int)poly.size() == 0)return false;

  rep(i,poly.size())
    if(onSegment(poly[i],poly[(i+1)%poly.size()],p))return true;
  double sum = 0;
  for(int i=0; i < (int)poly.size() ;i++)
    {
      if( equals(cross(poly[i]-p,poly[(i+1)%poly.size()]-p),0.0) ) continue;
      if(cross3p(p,poly[i],poly[(i+1)%poly.size()]) < 0) sum -= angle(p,poly[i],poly[(i+1)%poly.size()]);
      else sum += angle(p,poly[i],poly[(i+1)%poly.size()]);
    }
  const double eps = 1e-5;
  return (fabs(sum - 2*M_PI) < eps || fabs(sum + 2*M_PI) < eps);
}  

bool inPolygon(const Polygon &poly,Segment seg){
  vector<Point> vp;
  vp.push_back(seg.p1);
  vp.push_back(seg.p2);
  rep(i,(int)poly.size()) {
    Segment edge = Segment(poly[i],poly[(i+1)%(int)poly.size()]);
    if( equals(cross(seg.p1-seg.p2,edge.p1-edge.p2),0.0) ) { 
      if( onSegment(seg.p1,seg.p2,edge.p1) ) vp.push_back(edge.p1);
      if( onSegment(seg.p1,seg.p2,edge.p2) ) vp.push_back(edge.p2);
    } else if( intersectSS(seg,edge) ) vp.push_back(crosspoint(seg,edge));
  }
  sort(vp.begin(),vp.end());
  vp.erase(unique(vp.begin(),vp.end()),vp.end());
  rep(i,(int)vp.size()-1) {
    Point middle_point = ( vp[i] + vp[i+1] ) / 2.0;
    if( !inPolygon(poly,middle_point) ) return false;
  }
  return true;  
}

struct Node{
  int cur;
  double weight;
  bool operator < (const Node& node) const { return weight > node.weight; }
};

struct Edge{
  int from,to;
  double cost;
  Edge(int from=IINF,int to=IINF,double cost=IINF):from(from),to(to),cost(cost){}
  bool operator < (const Edge& a)const{ return cost < a.cost; }
};


const string NO = "impossible";
const int MAX_N = 110;
const int MAX_V = 100000;
int N;
Polygon polies[MAX_N];
Point sp,ep;
Line mirror;
double mindist[MAX_V];

bool  LT(double a,double b) { return !equals(a,b) && a < b; } 
bool LTE(double a,double b) { return  equals(a,b) || a < b; } 

//Point pを含む多角形のインデックスを返す,存在しない場合は-1
int selectGraph(Point p){
  rep(i,N) if( inPolygon(polies[i],p) ) return i;
  return -1;
}

void dijkstra(const vector<vector<Edge> > &G,const vector<Point> &ps){
  priority_queue<Node> Q;
  int start = -1, goal = -1, V = ps.size();
  assert( V < MAX_V );
  rep(i,V) {
    if( start == -1 && ps[i] == sp ) start = i;
    if( goal  == -1 && ps[i] == ep ) goal  = i;
    if( start != -1 && goal != -1  ) break;
  }
  rep(i,V) mindist[i] = 1e20;
  Q.push((Node){start,0});
  mindist[start] = 0;
  while( !Q.empty() ) {
    Node node = Q.top(); Q.pop();
    int cur = node.cur;
    double weight = node.weight;

    if( cur == goal ) {
      printf("%.12lf\n",weight);
      return;
    }

    if( LT(mindist[cur],weight) ) continue;
    rep(i,G[cur].size()){
      int to = G[cur][i].to;
      double new_weight =  weight + G[cur][i].cost;
      if( LT(new_weight,mindist[to]) ) {
        mindist[to] = new_weight;
        Q.push((Node){to,mindist[to]});
      }
    }
  }
  puts(NO.c_str());
}

void compute(){
  int indices[4] = {selectGraph(sp),selectGraph(ep),selectGraph(reflection(mirror,sp)),selectGraph(reflection(mirror,ep))};
  bool failed = false;
  rep(i,4) if( indices[i] == -1 ) { failed = true; break; }
  if( indices[0] != indices[1] || indices[2] != indices[3] ) failed = true;
  if( failed ) { puts(NO.c_str()); return; } 
  rep(i,N) if( i != indices[0] && i != indices[2] ) polies[i].clear();

  Polygon Real = polies[indices[0]];
  Polygon Mirr = polies[indices[2]];
  Polygon Mixi = Real;
  rep(i,(int)Mirr.size()) Mixi.push_back(reflection(mirror,Mirr[i]));
  Mixi.push_back(sp), Mixi.push_back(ep);  
  sort(Mixi.begin(),Mixi.end());
  Mixi.erase(unique(Mixi.begin(),Mixi.end()),Mixi.end());
 
  vector<Segment> segment_buffer;
  rep(i,(int)Mixi.size()) REP(j,i+1,(int)Mixi.size()) {
     Line line = Segment(Mixi[i],Mixi[j]);
    vector<Point> vp;
    vp.push_back(Mixi[i]);
    vp.push_back(Mixi[j]);
    rep(k,Real.size()) {
      Segment s = Segment(Real[k],Real[(k+1)%Real.size()]);
      if( equals(cross(s.p1-s.p2,line.p1-line.p2),0.0) ) {
        if( onSegment(line.p1,line.p2,s.p1) ) vp.push_back(s.p1);
        if( onSegment(line.p1,line.p2,s.p2) ) vp.push_back(s.p2);
      } else {
        if( intersectLS(line,s) )vp.push_back(crosspoint(line,s));
      }
    }
    sort(vp.begin(),vp.end());
    vp.erase(unique(vp.begin(),vp.end()),vp.end());
    rep(k,(int)vp.size()-1) {
      Segment  s = Segment(vp[k],vp[k+1]);
      Segment rs = Segment(reflection(mirror,s.p1),reflection(mirror,s.p2));
      if( inPolygon(Real,s) && inPolygon(Mirr,rs) ) segment_buffer.push_back(s);
    }
  }

  Mirr.clear(), Real.clear();
  sort(segment_buffer.begin(),segment_buffer.end());
  segment_buffer.erase(unique(segment_buffer.begin(),segment_buffer.end()),segment_buffer.end());
  int dex = 0;
  map<Point,int> mp;
  vector<Point> ps;
  rep(i,segment_buffer.size()) {
    if( !mp.count(segment_buffer[i].p1) ) {
      mp[segment_buffer[i].p1] = dex++;
      ps.push_back(segment_buffer[i].p1);
    }
    if( !mp.count(segment_buffer[i].p2) ) {
      mp[segment_buffer[i].p2] = dex++;
      ps.push_back(segment_buffer[i].p2);
    }
  }

  vector<vector<Edge> > G(dex,vector<Edge>());
  rep(i,segment_buffer.size()) {
    G[mp[segment_buffer[i].p1]].push_back(Edge(mp[segment_buffer[i].p1],mp[segment_buffer[i].p2],abs(segment_buffer[i].p1-segment_buffer[i].p2)));
    G[mp[segment_buffer[i].p2]].push_back(Edge(mp[segment_buffer[i].p2],mp[segment_buffer[i].p1],abs(segment_buffer[i].p1-segment_buffer[i].p2)));
  }
  dijkstra(G,ps);
}

int main(){
  while( cin >> N, N ){  
    rep(i,N){
      int M;
      cin >> M;
      polies[i].resize(M);
      rep(j,M) cin >> polies[i][j].x >> polies[i][j].y;
    }
    cin >> sp.x >> sp.y >> ep.x >> ep.y;
    cin >> mirror.p1.x >> mirror.p1.y >> mirror.p2.x >> mirror.p2.y;
    compute();
  }
  return 0;
}

Measured memory_bytes: 3568