CF469B.Chat Online

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?

小 X 和小 Z 是好朋友，他们经常在线聊天。但两人都有自己的日程安排。

小 Z 的日程是固定的：他在时间区间 $[a_1, b_1]$、$[a_2, b_2]$、……、$[a_p, b_p]$（所有端点均包含在内）的任意时刻都在线。

而小 X 的日程则非常特殊，它取决于他起床的时间。若他在时刻 $0$ 起床，则他在时间区间 $[c_1, d_1]$、$[c_2, d_2]$、……、$[c_q, d_q]$（所有端点均包含在内）的任意时刻都在线；若他在时刻 $t$ 起床，则这些区间将整体向右平移 $t$，即变为 $[c_i + t,\, d_i + t]$（对所有 $i$）。

若在某一时刻，小 X 和小 Z 同时在线，则他们可以愉快地在线聊天。已知小 X 可以在整数时刻 $t$ 起床，且 $t$ 的取值范围为 $[l,\, r]$（两端点均包含在内）。此外，小 X 希望选择一个能与小 Z 成功聊天的起床时刻（即两人的在线时间至少存在一个公共时刻）。问：在区间 $[l,\, r]$ 中，有多少个整数时刻 $t$ 满足该条件？

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 a__i, b__i (0 ≤ a__i < b__i ≤ 1000). Each of the next q lines contains two space-separated integers c__j, d__j (0 ≤ c__j < d__j ≤ 1000).

It's guaranteed that b__i < a__i + 1 and d__j < c__j + 1 for all valid i and j.

第一行包含四个以空格分隔的整数 $p$、$q$、$l$、$r$（$1 \le p, q \le 50$；$0 \le l \le r \le 1000$）。

接下来的 $p$ 行，每行包含两个以空格分隔的整数 $a_i$、$b_i$（$0 \le a_i < b_i \le 1000$）。再接下来的 $q$ 行，每行包含两个以空格分隔的整数 $c_j$、$d_j$（$0 \le c_j < d_j \le 1000$）。

保证对所有合法的 $i$ 和 $j$，均有 $b_i < a_i + 1$ 且 $d_j < c_j + 1$。

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

输出一个整数——即区间 ([l, r]) 中适合进行在线聊天的时间点的个数。