// OB���h2009 Day3 I : Wind Passages

#include <iostream>
#include <complex>
#include <vector>

using namespace std;

const double EPS = 1e-7;
typedef complex<double> P;
typedef vector<P> G;
struct L { P p, q; L(P p, P q) : p(p), q(q) {} };
double dot(P a, P b) { return real(conj(a)*b); }
double cross(P a, P b) { return imag(conj(a)*b); }

double distLP(L l, P p){
	if(dot(l.q-l.p,p-l.p)<-EPS) return abs(p-l.p);
	if(dot(l.p-l.q,p-l.q)<-EPS) return abs(p-l.q);
	return abs(cross(l.q-l.p,p-l.p))/abs(l.q-l.p);
}

double distLL(L l, L m){
	double res = distLP(l, m.p);
	res = min(res, distLP(l, m.q));
	res = min(res, distLP(m, l.p));
	res = min(res, distLP(m, l.q));
	return res;
}

double distCC(G g1, G g2){
	double res = 1e12;
	for(int i=0;i<g1.size();i++){
		for(int j=0;j<g2.size();j++){
			res = min(res, distLL(L(g1[i],g1[(i+1)%g1.size()]),L(g2[j],g2[(j+1)%g2.size()])));
		}
	}
	return res;
}

int main(){
	double d1[200], d2[200];
	double dist[200][200];
	int w, n;
	while(cin >> w >> n, w){
		for(int i=0;i<n;i++){
			for(int j=0;j<n;j++) dist[i][j] = 1e12;
			dist[i][i] = 0.0;
		}
		vector<G> vg;
		G vd1, vd2;
		vd1.push_back(P(0,-100));
		vd1.push_back(P(0,20000));
		vd2.push_back(P(w,-100));
		vd2.push_back(P(w,20000));
		for(int i=0;i<n;i++){
			G g;
			int m; cin >> m;
			for(int j=0;j<m;j++){
				int x, y; cin >> x >> y;
				g.push_back(P(x,y));
			}
			vg.push_back(g);
		}
		for(int i=0;i<n;i++){
			d1[i] = distCC(vd1,vg[i]);
			d2[i] = distCC(vd2,vg[i]);
		}
		for(int i=0;i<n;i++){
			for(int j=i+1;j<n;j++){
				dist[i][j] = distCC(vg[i],vg[j]);
				dist[j][i] = dist[i][j];
			}
		}
		for(int j=0;j<n;j++)
			for(int i=0;i<n;i++)
				for(int k=0;k<n;k++)
					dist[i][k] = min(dist[i][k], dist[i][j]+dist[j][k]);
		double ans = w;
		for(int i=0;i<n;i++){
			for(int j=0;j<n;j++){
				ans = min(ans, d1[i]+dist[i][j]+d2[j]);
			}
		}
		printf("%.8lf\n", ans);
	}
}