Little X and Little Z are good friends. They always chat online. But both of them have schedules. Little Z has fixed schedule. He always online at any moment of time between a 1 and b 1 , between a 2 and b 2 , ..., between a p and b p (all borders inclusive). But the schedule of Little X is quite strange, it depends on the time when he gets up. If he gets up at time 0, he will be online at any moment of time between c 1 and d 1 , between c 2 and d 2 , ..., between c q and d q (all borders inclusive). But if he gets up at time t , these segments will be shifted by t . They become [c i + t, d i + t] (for all i ). If at a moment of time, both Little X and Little Z are online simultaneosly, they can chat online happily. You know that Little X can get up at an integer moment of time between l and r (both borders inclusive). Also you know that Little X wants to get up at the moment of time, that is suitable for chatting with Little Z (they must have at least one common moment of time in schedules). How many integer moments of time from the segment [l, r] suit for that?

输入描述:

The first line contains four space-separated integers p, q, l, r (1 ≤ p, q ≤ 50; 0 ≤ l ≤ r ≤ 1000).Each of the next p lines contains two space-separated integers ai, bi (0 ≤ ai bi ≤ 1000). Each of the next q lines contains two space-separated integers cj, dj (0 ≤ cj dj ≤ 1000).It's guaranteed that bi ai + 1 and dj cj + 1 for all valid i and j.

输出描述:

Output a single integer — the number of moments of time from the segment [l, r] which suit for online conversation.