#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, a, b, finish1 = INFINITY, finish2 = INFINITY, start1 = 0,
                     start2 = 0, mx = 0;
  scanf("%lld", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%lld %lld", &a, &b);
    start2 = max(start2, a);
    finish1 = min(finish1, b);
  }
  scanf("%lld", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%lld %lld", &a, &b);
    start1 = max(start1, a);
    finish2 = min(finish2, b);
  }
  mx = max(mx, start1 - finish1);
  mx = max(mx, start2 - finish2);
  if (mx <= 0)
    printf("0\n");
  else
    printf("%lld\n", mx);
  return 0;
}
