#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <valarray>
#include <vector>

#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define fir first
#define foreach(it,X) for(__typeof((X).begin()) it=(X).begin();it!=(X).end();it++)
#define ite iterator
#define mp make_pair
#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<(n);i++)
#define pb push_back
#define sec second
#define sz(x) ((int)(x).size())

using namespace std;

struct timer{
	time_t start;
	timer(){start=clock();}
	~timer(){cerr<<1.*(clock()-start)/CLOCKS_PER_SEC<<" secs"<<endl;}
};

typedef istringstream iss;
typedef long long ll;
typedef pair<int,int> pi;
typedef stringstream sst;
typedef vector<int> vi;

#define PI 3.14159265358979323846

#define curr(P, i) P[(i) % P.size()]
#define next(P, i) P[(i+1) % P.size()]
#define prev(P, i) P[(i+P.size()-1) % P.size()]
#define diff(P, i) (next(P,i) - curr(P,i))
#define EQ(x,y) (fabs((x)-(y))<EPS)
#define GE(x,y) ((x)+EPS>(y))
#define LE(x,y) ((x)<(y)+EPS)
enum { OUT, ON, IN };

typedef complex<double> P;
typedef vector<P> G;

namespace std{
  bool operator < (const P& a, const P& b) {
    return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
  }
}

double cross(const P& a, const P& b) {
  return imag(conj(a)*b);
}
double dot(const P& a, const P& b) {
  return real(conj(a)*b);
}

struct L : public vector<P> {
  L(){}
  L(const P &a, const P &b) {
    push_back(a); push_back(b);
  }
};

struct C {
  P p; double r;
  C(const P &p, double r) : p(p), r(r) { }
};

int ccw(P a, P b, P c) {
  b -= a; c -= a;
  if (cross(b, c) > EPS)   return +1;       // counter clockwise
  if (cross(b, c) < -EPS)   return -1;       // clockwise
  if (dot(b, c) < -EPS)     return +2;       // c--a--b on line
  if (norm(b) < norm(c)+EPS) return -2;       // a--b--c on line
  return 0;
}

bool intersectLL(const L &l, const L &m) {
  return abs(cross(l[1]-l[0], m[1]-m[0])) > EPS || // non-parallel
         abs(cross(l[1]-l[0], m[0]-l[0])) < EPS;   // same line
}
bool intersectLS(const L &l, const L &s) {
  return cross(l[1]-l[0], s[0]-l[0])*       // s[0] is left of l
         cross(l[1]-l[0], s[1]-l[0]) < EPS; // s[1] is right of l
}
bool intersectLP(const L &l, const P &p) {
  return abs(cross(l[1]-p, l[0]-p)) < EPS;
}
bool intersectSS(const L &s, const L &t) {
  return ccw(s[0],s[1],t[0])*ccw(s[0],s[1],t[1]) <= 0 &&
         ccw(t[0],t[1],s[0])*ccw(t[0],t[1],s[1]) <= 0;
}
bool intersectSP(const L &s, const P &p) {
  return abs(s[0]-p)+abs(s[1]-p)-abs(s[1]-s[0]) < EPS; // triangle inequality
}

P projection(const L &l, const P &p) {
  double t = dot(p-l[0], l[0]-l[1]) / norm(l[0]-l[1]);
  return l[0] + t*(l[0]-l[1]);
}
P reflection(const L &l, const P &p) {
  return p + 2.0 * (projection(l, p) - p);
}
double distanceLP(const L &l, const P &p) {
  return abs(p - projection(l, p));
}
double distanceLL(const L &l, const L &m) {
  return intersectLL(l, m) ? 0 : distanceLP(l, m[0]);
}
double distanceLS(const L &l, const L &s) {
  if (intersectLS(l, s)) return 0;
  return min(distanceLP(l, s[0]), distanceLP(l, s[1]));
}
double distanceSP(const L &s, const P &p) {
  const P r = projection(s, p);
  if (intersectSP(s, r)) return abs(r - p);
  return min(abs(s[0] - p), abs(s[1] - p));
}
double distanceSS(const L &s, const L &t) {
  if (intersectSS(s, t)) return 0;
  return min(min(distanceSP(s, t[0]), distanceSP(s, t[1])),
             min(distanceSP(t, s[0]), distanceSP(t, s[1])));
}
P crosspoint(const L &l, const L &m) {
  double A = cross(l[1] - l[0], m[1] - m[0]);
  double B = cross(l[1] - l[0], l[1] - m[0]);
  if (abs(A) < EPS && abs(B) < EPS) return m[0]; // same line
  if (abs(A) < EPS) assert(false); // !!!PRECONDITION NOT SATISFIED!!!
  return m[0] + B / A * (m[1] - m[0]);
}

double W;
int N;
vector<L> g[222];
double dist[222][222];

int main(){
	cin.tie(0);
	ios_base::sync_with_stdio(0);
	
	while(cin>>W>>N && W){
		rep(i,N+2)g[i].clear();
		g[0].pb(L(P(0,0),P(0,10000)));
		g[1].pb(L(P(W,0),P(W,10000)));
		rep2(i,2,N+2){
			int M;
			cin>>M;
			vector<P> p;
			rep(j,M){
				double x,y;
				cin>>x>>y;
				p.pb(P(x,y));
			}
			rep(j,M){
				g[i].pb(L(curr(p,j),next(p,j)));
			}
		}
		N+=2;
		rep(i,N)rep(j,N)dist[i][j]= i==j?0:INF;
		rep(i,N)rep2(j,i+1,N){
			rep(k,sz(g[i]))rep(l,sz(g[j])){
				dist[i][j]=dist[j][i]= min(dist[i][j],distanceSS(g[i][k],g[j][l]));
			}
		}
		rep(k,N)rep(i,N)rep(j,N)dist[i][j]=min(dist[i][j],dist[i][k]+dist[k][j]);
		cout<<fixed<<setprecision(16)<<dist[0][1]<<endl;
	}
}

Measured memory_bytes: 1744