Zombies

4000ms

262144K

Description:

Polycarp plays a computer game in a post-apocalyptic setting. The zombies have taken over the world, and Polycarp with a small team of survivors is defending against hordes trying to invade their base. The zombies are invading for $$$x$$$ minutes starting from minute $$$0$$$. There are $$$n$$$ entrances to the base, and every minute one zombie attempts to enter through every entrance.

The survivors can defend the entrances against the zombies. There are two options:

manually — shoot the zombies coming through a certain entrance;
automatically — set up an electric fence on a certain entrance to fry the zombies.

If an entrance is defended either or both ways during some minute, no zombie goes through.

Every entrance is defended by a single dedicated survivor. The $$$i$$$-th entrance is defended manually from minute $$$l_i$$$ until minute $$$r_i$$$, non-inclusive — $$$[l_i, r_i)$$$.

There are $$$k$$$ generators that can be used to defend the entrances automatically. Every entrance should be connected to exactly one generator, but a generator can be connected to multiple entrances (or even none of them). Each generator will work for exactly $$$m$$$ consecutive minutes. Polycarp can choose when to power on each generator independently of each other, the $$$m$$$ minute long interval should be fully inside the $$$[0, x)$$$ time interval.

Polycarp is a weird gamer. He wants the game to be as difficult as possible for him. So he wants to connect each entrance to a generator and choose the time for each generator in such a way that as many zombies as possible enter the base. Please, help him to achieve that!

Input:

The first line contains four integers $$$n, k, x$$$ and $$$m$$$ ($$$1 \le k \le n \le 2000$$$; $$$1 \le m \le x \le 10^9$$$) — the number of entrances, the number of generators, the duration of the zombie invasion and the duration of all generators.

The $$$i$$$-th of the next $$$n$$$ lines contains two integers $$$l_i$$$ and $$$r_i$$$ ($$$0 \le l_i < r_i \le x$$$) — the time interval the $$$i$$$-th entrance is defended manually.

Output:

Print a single integer — the largest number of zombies that can enter the base after Polycarp connects each entrance to some generator and chooses the time for each generator.

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2 1 20 6
11 13
2 14

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Informação

Provedor Codeforces

Código CF1832F