#include <iostream>
 
using namespace std;
 
int n, m;
pair<int,int> a[200005], b[200005];
 
int main(){
	cin >> n;
	int mx1=-1, mn1=1000000009, mx2=-1, mn2=1000000009;
	for (int i = 1; i <= n; i++){
		cin >> a[i].first >> a[i].second;
		if (a[i].first>mx1) mx1 = a[i].first;
		if (a[i].second<mn1) mn1 = a[i].second; 
	//	orga[i] = a[i];
	}
	cin >> m;
	for (int i = 1; i <= m; i++){
		cin >> b[i].first >> b[i].second;
		if (b[i].first>mx2) mx2 = b[i].first;
		if (b[i].second<mn2) mn2= b[i].second;
	//	orgb[i] = b[i];
	}
	int r1 = mx1-mn2;
	int r2 = mx2-mn1;
	int mx = max(r1, r2);
	if (mx <= 0) cout << 0;
	else cout << mx;
	return 0;
}

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