/*
  submitted from Malaysia
  
 */
#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-10)
#define equals(a,b) (fabs((a)-(b)) < EPS)
#define COUNTER_CLOCKWISE 1
#define CLOCKWISE -1 
#define ONLINE_BACK 2
#define ONLINE_FRONT -2
#define ON_SEGMENT 0

using namespace std;

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);}
  Point operator * (Point a){ return Point(x * a.x - y * a.y, x * a.y + y * a.x); }

  bool operator < (const Point& p) const{ return !equals(x,p.x)?x<p.x:(!equals(y,p.y)&&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& s) const { return ( p2 == s.p2 ) ? p1 < s.p1 : p2 < s.p2; }
  bool operator == (const Segment& s) const { return ( s.p1 == p1 && s.p2 == p2 ) || ( s.p1 == p2 && s.p2 == p1 ); }

};

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

ostream& operator << (ostream& os,const Point& a){ os << "(" << a.x << "," << a.y << ")"; }

ostream& operator << (ostream& os,const Segment& a){ os << "( " << a.p1 << " , " << a.p2 << " )"; }

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)); }

//rad は角度をラジアンで持たせること
Point rotate(Point a,double rad){ return Point(cos(rad)*a.x - sin(rad)*a.y,sin(rad)*a.x + cos(rad)*a.y); }

// 度をラジアンに変換
double toRad(double agl){ return agl*M_PI/180.0; }

// a => prev, b => cur, c=> next
// prev から cur へ行って next へ行く際の角度を求める
double getArg(Point a,Point b,Point c){
  double arg1 = atan2(b.y-a.y,b.x-a.x);
  double arg2 = atan2(c.y-b.y,c.x-b.x);
  double arg = fabs( arg1 - arg2 );
  while( arg > M_PI ) arg -= 2.0 * M_PI;
  return fabs(arg);
}

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 intersectLL(Line l, Line m) {
  return abs(cross(l.p2-l.p1, m.p2-m.p1)) > EPS || // non-parallel
         abs(cross(l.p2-l.p1, m.p1-l.p1)) < EPS;   // same line
}
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 intersectLP(Line l,Point p) {
  return abs(cross(l.p2-p, l.p1-p)) < EPS;
}
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;
}
bool intersectSP(Line s, Point p) {
  return abs(s.p1-p)+abs(s.p2-p)-abs(s.p2-s.p1) < EPS; // triangle inequality
}

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;
}
double distanceLP(Line l, Point p) {
  return abs(p - projection(l, p));
}
double distanceLL(Line l, Line m) {
  return intersectLL(l, m) ? 0 : distanceLP(l, m.p1);
}

double distanceLS(Line l, Line s) {
  if (intersectLS(l, s)) return 0;
  return min(distanceLP(l, s.p1), distanceLP(l, s.p2));
}
double distanceSP(Line s, Point p) {
  Point r = projection(s, p);
  if (intersectSP(s, r)) return abs(r - p);
  return min(abs(s.p1 - p), abs(s.p2 - p));
}

double distanceSS(Line s, Line t) {
  if (intersectSS(s, t)) return 0;
  return min(min(distanceSP(s, t.p1), distanceSP(s, t.p2)),
             min(distanceSP(t, s.p1), distanceSP(t, s.p2)));
}

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;
  }
  if(abs(A) < EPS)assert(false);
  return m.p1 + (m.p2-m.p1)*(B/A);
}

//pとsの距離が最小となるようなs上の点を返す
Point getNearestPoint(Segment s,Point p){
  double mini = distanceSP(s,p);
  if( equals(mini,0) ) return p;
  Point r = projection(s,p);
  if( intersectSP(s,r) ) return r;
  if( equals(mini,abs(s.p1-p)) ) return s.p1;
  return s.p2;
}

// 2つの線分が与えられた時、それらの線分間の距離が最小となるような線分を返す
Segment getNearestSegment(Segment s,Segment t){
  if( intersectSS(s,t) ) return crosspoint(s,t);
  double mini = distanceSS(s,t);
  if( equals(mini,distanceSP(s,t.p1)) ) {
    return Segment(t.p1,getNearestPoint(s,t.p1));
  }

  if( equals(mini,distanceSP(s,t.p2)) ) {
    return Segment(t.p2,getNearestPoint(s,t.p2));
  } 

  if( equals(mini,distanceSP(t,s.p1)) ) {
    return Segment(s.p1,getNearestPoint(t,s.p1));
  } 

  if( equals(mini,distanceSP(t,s.p2)) ) {
    return Segment(s.p2,getNearestPoint(t,s.p2));
  } 
  assert(false);
}

//cross product of pq and pr
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); }
  
//returns true if point r is on the same line as the line pq
bool collinear(Point p,Point q,Point r) { return fabs(cross3p(p,q,r)) < EPS; }
  
//returns true if point t is on the left side of line pq
bool ccwtest(Point p,Point q,Point r){
  return cross3p(p,q,r) > 0; //can be modified to accept collinear points
}
 
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)) ) ;
}
  

bool isConvex(vector<Point> p) {
  int sz = (int)p.size();
  if(sz < 3)return false;//boundary case, we treat a point or a line as not convex
  bool isLeft = ccwtest(p[0],p[1],p[2]);
  for(int i=1; i<(int)p.size();i++)
    if(ccwtest(p[i],p[(i+1)%sz],p[(i+2)%sz]) != isLeft) return false;
  return true;
}


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)));
}  
  
//多角形poly内（線分上も含む）に点pが存在するかどうは判定する  
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; // ３点が平行だとangleがnanを返しsumがnanになり死ぬ
    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()]);
  }
  // あまり誤差を厳しくしすぎると良くないので以下のほうが良い 
  const double eps = 1e-5;
  return (fabs(sum - 2*M_PI) < eps || fabs(sum + 2*M_PI) < eps);
}  

struct Edge { int to; double weight; };

int W,N;

struct Data { 
  int cur;
  double cost;
  bool operator < ( const Data &data ) const {
    if( !equals(cost,data.cost) ) return cost > data.cost;
    return cur > data.cur;
  }
};

const int MAX = 500;
double mindist[MAX];

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

double dijkstra(int s,int t,vector<vector<Edge> > &G){
  priority_queue<Data> Q;
  rep(i,G.size()) mindist[i] = 1e20;
  Q.push((Data){s,0});
  mindist[s] = 0; 
  while( !Q.empty() ) {
    Data data = Q.top(); Q.pop();
    if( data.cur == t ) return data.cost;
    rep(i,(int)G[data.cur].size()){
      int next = G[data.cur][i].to;
      if( LT(data.cost+G[data.cur][i].weight,mindist[next]) ) {
	mindist[next] = data.cost+G[data.cur][i].weight;
	Q.push((Data){next,mindist[next]});
      }
    }
  }
  return 1e20;
}

void compute(vector<Polygon> &polies){
  int sp = N;
  int ep = sp + 1;
  Line s = Line(Point(0,0),Point(0,10)); 
  Line t = Line(Point(W,0),Point(W,10));
  vector<vector<Edge> > G(N+2);
  
  G[sp].push_back((Edge){ep,W});
  G[ep].push_back((Edge){sp,W});

  rep(i,polies.size()) {
    double mini = 1e20;
    rep(j,polies[i].size()) mini = min(mini,distanceLS(s,Segment(polies[i][j],polies[i][(j+1)%polies[i].size()])));
    G[sp].push_back((Edge){i,mini});
    G[i].push_back((Edge){sp,mini});
  }
  rep(i,polies.size()) {
    double mini = 1e20;
    rep(j,polies[i].size()) mini = min(mini,distanceLS(t,Segment(polies[i][j],polies[i][(j+1)%polies[i].size()])));
    G[ep].push_back((Edge){i,mini});
    G[i].push_back((Edge){ep,mini});
  }
  rep(i,polies.size()) REP(j,i+1,polies.size()) {
    double mini = 1e20;
    rep(k,polies[i].size()) rep(l,polies[j].size()) mini = min(mini,
							       distanceSS(Segment(polies[i][k],polies[i][(k+1)%polies[i].size()]),Segment(polies[j][l],polies[j][(l+1)%polies[j].size()])));
    G[i].push_back((Edge){j,mini});
    G[j].push_back((Edge){i,mini});
  }
  printf("%.10f\n",dijkstra(sp,ep,G));
}

int main(){ 
  while( cin >> W >> N , W|N ){
    vector<Polygon> polies(N);
    rep(i,N){
      int V;
      cin >> V;
      polies[i].clear();
      polies[i].resize(V);
      rep(j,V) cin >> polies[i][j].x >> polies[i][j].y;
    }
    compute(polies);
  }
  return 0;
}

Measured memory_bytes: 2532