Realistic Gameplay

题意翻译

有$n$波怪物，你有一把枪，枪的弹夹量为$k$，第$i$波怪物数量为$a_i$，在第$l_i$到$r_i$时间出现（$r_i<=l_{i+1}$），你可以在任意时刻打出一发子弹击杀一只怪物且不耗费时间，你必须在$[l_i, r_i]$时间内消灭$a_i$只怪物，你每次换弹都需要将弹夹（包括里面的子弹）扔掉，并花费 1 单位的时间，在尽量保证通关的情况下，需要的最少的子弹数为多少

题目描述

Recently you've discovered a new shooter. They say it has realistic game mechanics. Your character has a gun with magazine size equal to $ k $ and should exterminate $ n $ waves of monsters. The $ i $ -th wave consists of $ a_i $ monsters and happens from the $ l_i $ -th moment of time up to the $ r_i $ -th moments of time. All $ a_i $ monsters spawn at moment $ l_i $ and you have to exterminate all of them before the moment $ r_i $ ends (you can kill monsters right at moment $ r_i $ ). For every two consecutive waves, the second wave starts not earlier than the first wave ends (though the second wave can start at the same moment when the first wave ends) — formally, the condition $ r_i \le l_{i + 1} $ holds. Take a look at the notes for the examples to understand the process better. You are confident in yours and your character's skills so you can assume that aiming and shooting are instant and you need exactly one bullet to kill one monster. But reloading takes exactly $ 1 $ unit of time. One of the realistic mechanics is a mechanic of reloading: when you reload you throw away the old magazine with all remaining bullets in it. That's why constant reloads may cost you excessive amounts of spent bullets. You've taken a liking to this mechanic so now you are wondering: what is the minimum possible number of bullets you need to spend (both used and thrown) to exterminate all waves. Note that you don't throw the remaining bullets away after eradicating all monsters, and you start with a full magazine.

输入输出格式

输入格式

The first line contains two integers $ n $ and $ k $ ( $ 1 \le n \le 2000 $ ; $ 1 \le k \le 10^9 $ ) — the number of waves and magazine size. The next $ n $ lines contain descriptions of waves. The $ i $ -th line contains three integers $ l_i $ , $ r_i $ and $ a_i $ ( $ 1 \le l_i \le r_i \le 10^9 $ ; $ 1 \le a_i \le 10^9 $ ) — the period of time when the $ i $ -th wave happens and the number of monsters in it. It's guaranteed that waves don't overlap (but may touch) and are given in the order they occur, i. e. $ r_i \le l_{i + 1} $ .

输出格式

If there is no way to clear all waves, print $ -1 $ . Otherwise, print the minimum possible number of bullets you need to spend (both used and thrown) to clear all waves.

输入输出样例

输入样例 #1

2 3
2 3 6
3 4 3

输出样例 #1

9

输入样例 #2

2 5
3 7 11
10 12 15

输出样例 #2

30

输入样例 #3

5 42
42 42 42
42 43 42
43 44 42
44 45 42
45 45 1

输出样例 #3

-1

输入样例 #4

1 10
100 111 1

输出样例 #4

1

说明

In the first example: - At the moment $ 2 $ , the first wave occurs and $ 6 $ monsters spawn. You kill $ 3 $ monsters and start reloading. - At the moment $ 3 $ , the second wave occurs and $ 3 $ more monsters spawn. You kill remaining $ 3 $ monsters from the first wave and start reloading. - At the moment $ 4 $ , you kill remaining $ 3 $ monsters from the second wave. In total, you'll spend $ 9 $ bullets.In the second example: - At moment $ 3 $ , the first wave occurs and $ 11 $ monsters spawn. You kill $ 5 $ monsters and start reloading. - At moment $ 4 $ , you kill $ 5 $ more monsters and start reloading. - At moment $ 5 $ , you kill the last monster and start reloading throwing away old magazine with $ 4 $ bullets. - At moment $ 10 $ , the second wave occurs and $ 15 $ monsters spawn. You kill $ 5 $ monsters and start reloading. - At moment $ 11 $ , you kill $ 5 $ more monsters and start reloading. - At moment $ 12 $ , you kill last $ 5 $ monsters. In total, you'll spend $ 30 $ bullets.