#include<cstdio>

#include<cmath>

#include<algorithm>

using namespace std;

const int N=50010;

const double eps=1e-9;

inline int sgn(double x){

  if(x<-eps)return -1;

  if(x>eps)return 1;

  return 0;

}

int n,m,i;double l,r,mid,f[N],da[N],db[N];

struct P{

  double x,y;

  P(){}

  P(double _x,double _y){x=_x,y=_y;}

  P operator+(const P&b){return P(x+b.x,y+b.y);}

  P operator-(const P&b){return P(x-b.x,y-b.y);}

  P operator*(double b){return P(x*b,y*b);}

  P operator/(double b){return P(x/b,y/b);}

  double operator*(const P&b){return x*b.x+y*b.y;}

  double len(){return hypot(x,y);}

  void read(){scanf("%lf%lf",&x,&y);}

}a[N],b[N];

inline double cross(P a,P b){return a.x*b.y-a.y*b.x;}

inline P lerp(P a,P b,double t){return a*(1.0-t)+b*t;}

inline double dist_point_to_segment(P p,P a,P b){

  if((b-a).len()>eps&&sgn((p-a)*(b-a))>=0&&sgn((p-b)*(a-b))>=0)return fabs(cross(p-a,b-a))/(b-a).len();

  return min((p-a).len(),(p-b).len());

}

inline double cal(P A,P B,P C,P D,double t){

  B=B-A;

  B=B/B.len();

  D=D-C;

  D=D/D.len();

  D=D-B;

  return dist_point_to_segment(A,C,C+D*t);

}

bool check(double mid){

  int i=1,j;

  P A=a[1],B;

  double v=0,w;

  for(j=1;j<m;j++)if(mid<f[j]){

    w=mid-f[j-1];

    B=lerp(b[j],b[j+1],w/db[j]);

    break;

  }

  if(j==m)return 1;

  while(i<n&&j<m){

    double x=(A-a[i+1]).len(),y=(B-b[j+1]).len();

    if((A-B).len()<mid+eps)return 1;

    if(x>eps&&y>eps)if(cal(A,a[i+1],B,b[j+1],min(x,y))<mid+eps)return 1;

    if(!sgn(x-y)){

      A=a[++i];

      B=b[++j];

      v=w=0;

      continue;

    }

    if(x<y){

      A=a[++i];

      v=0;

      w+=x;

      B=lerp(b[j],b[j+1],w/db[j]);

      continue;

    }

    v+=y;

    A=lerp(a[i],a[i+1],v/da[i]);

    B=b[++j];

    w=0;

  }

  return 0;

}

int main(){

  scanf("%d",&n);

  for(i=1;i<=n;i++)a[i].read();

  scanf("%d",&m);

  for(i=1;i<=m;i++)b[i].read();

  for(i=1;i<n;i++)da[i]=(a[i]-a[i+1]).len();

  for(i=1;i<m;i++)db[i]=(b[i]-b[i+1]).len();

  for(i=1;i<m;i++)f[i]=f[i-1]+db[i];

  r=f[m-1];

  if((a[1]-b[m]).len()>r+eps)return puts("impossible"),0;

  for(i=40;i;i--)if(check(mid=(l+r)/2))r=mid;else l=mid;

  return printf("%.8f",(l+r)/2),0;

}