#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
#include <stack>
#include <cmath>
#define int long long
#define double long double
using namespace std;

void read(int &x){
	x=0;
	int f=1;
	char c=getchar();
	while(!('0'<=c && c<='9')){
		if(c=='-'){
			f=-1;
		}
		c=getchar();
	} 
	while('0'<=c && c<='9'){
		x=(x<<3)+(x<<1)+(c^48);
		c=getchar();
	}
	x*=f;
}
struct Vector{
	double x,y;
	Vector(){
		x=y=0;
	}
	Vector(double xx,double yy){
		x=xx;
		y=yy;
	}
	friend Vector operator+(Vector a,Vector b){
		return Vector(a.x+b.x,a.y+b.y);
	}
	friend Vector operator-(Vector a,Vector b){
		return Vector(a.x-b.x,a.y-b.y);
	}
	friend Vector operator*(Vector a,double c){
		return Vector(a.x*c,a.y*c);
	}
	friend double operator*(Vector a,Vector b){
		return a.x*b.y-a.y*b.x;
	}
	double length(){
		return sqrt(x*x+y*y);
	}
	void show(){
		printf("(%Lf %Lf)",x,y);
	}
} pa[1000010],pb[1000010],sa[1000010],sb[1000010];
int n,m;
double da[1000010],db[1000010];
double getd(Vector a,Vector b){
//	printf("[%lf %lf]->[%lf %lf]\n",a.x,a.y,b.x,b.y);
	Vector ab=a-b,norm=Vector(ab.y,-ab.x);
	if(ab.length()<=1e-9){
		return a.length();
	}
	if((a*norm)*(norm*b)<0){
		return min(a.length(),b.length());
	}else{
		return abs((a*b))/(ab.length());
	}
}
bool chk(double t){
	int posa=1,posb=1;
	double lsta=0,lstb=t;
	Vector cura=pa[0],curb=pb[0];
	for(int i=1;i<=m;i++){
		if(db[i]<t){
			curb=pb[i];
		}else{
			curb=curb+sb[i]*(t-db[i-1]);
			posb=i;
			break;
		}
	}
	while(1){
		if(posa==n+1 || posb==m+1){
			break;
		}
		if(da[posa]>db[posb]-t){
//			printf("[%Lf]",db[posb]-t);
//			cura.show();
//			curb.show();
//			putchar('\n');
			if(getd(cura-curb,cura+sa[posa]*(db[posb]-t-lsta)-curb-sb[posb]*(db[posb]-lstb))<=t+1e-6){
				return 1;
			}
			cura=cura+sa[posa]*(db[posb]-t-lsta);
			curb=curb+sb[posb]*(db[posb]-lstb);
			lsta=db[posb]-t;
			lstb=db[posb];
			posb++;
		}else{
//			printf("[%Lf]",da[posa]);
//			cura.show();
//			curb.show();
//			putchar('\n');
			if(getd(cura-curb,cura+sa[posa]*(da[posa]-lsta)-curb-sb[posb]*(da[posa]+t-lstb))<=t+1e-6){
				return 1;
			}
			cura=cura+sa[posa]*(da[posa]-lsta);
			curb=curb+sb[posb]*(da[posa]+t-lstb);
			lsta=da[posa];
			lstb=da[posa]+t;
			posa++;
		}
	}
	return 0;
}
signed main(){
	read(n);
	n--;
	for(int i=0;i<=n;i++){
		scanf("%Lf %Lf",&pa[i].x,&pa[i].y);
		if(i){
			sa[i]=(pa[i]-pa[i-1])*(1.0/(pa[i]-pa[i-1]).length());
			da[i]=da[i-1]+(pa[i]-pa[i-1]).length();
		}
	}
	read(m);
	m--;
	da[0]=db[0]=0;
	for(int i=0;i<=m;i++){
		scanf("%Lf %Lf",&pb[i].x,&pb[i].y);
		if(i){
			sb[i]=(pb[i]-pb[i-1])*(1.0/(pb[i]-pb[i-1]).length());
			db[i]=db[i-1]+(pb[i]-pb[i-1]).length();
		}
	}
	if((pa[0]-pb[m]).length()>db[m]){
		printf("impossible");
		return 0;
	}
	da[n+1]=db[m+1]=4e18;
	double ql=0,qr=db[m];
	while(ql<qr-1e-9){
		double mid=(ql+qr)/2;
		if(chk(mid)){
			qr=mid;
		}else{
			ql=mid;
		}
	}
	printf("%.9Lf",ql);
	return 0;
}