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 a₁ and b₁, between a₂ and b₂, ..., 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 c₁ and d₁, between c₂ and d₂, ..., 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?

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.

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

1 1 0 4
2 3
0 1

3

2 3 0 20
15 17
23 26
1 4
7 11
15 17

20