#include <cstdio>

#include <cmath>

#include <cstring>

#include <map>

#include <algorithm>

using namespace std;

int n,m;

int a,b,c,d;

int main()

{

	scanf("%d",&n);

	for(int i=1;i<=n;i++)

	{

		int x,y; scanf("%d%d",&x,&y);

		if(i==1) a=y; else a = min(a,y);

		if(i==1) c=x; else c = max(c,x);

	}

	scanf("%d",&m);

	for(int i=1;i<=m;i++)

	{

		int x,y; scanf("%d%d",&x,&y);

		if(i==1) b=x; else b = max(b,x);

		if(i==1) d=y; else d = min(d,y);

	}

	printf("%d\n",max(max(b-a,0),max(c-d,0)));

	return 0;

}