time limit per test: 1 second
memory limit per test: 256 megabytes
input: standard input
output: standard output
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 ap and bp (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 cq and dq (all
borders inclusive). But if he gets up at time t, these
segments will be shifted by t. They
become [ci + t, di + 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?
Input
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.
Output
Output a single
integer — the number of moments of time from the segment [l, r] which
suit for online conversation.
Examples
input
1 1 0 4
2 3
0 1
2 3
0 1
output
3
input
2 3 0 20
15 17
23 26
1 4
7 11
15 17
15 17
23 26
1 4
7 11
15 17
output
20
