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? 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.