Problem:
Score : 600 points

Problem Statement

Silver Fox is fighting with N monsters.

The monsters are standing in a row, and we can assume them to be standing on a number line. The i-th monster, standing at the coordinate X_i, has the health of H_i.

Silver Fox can use bombs to attack the monsters.
Using a bomb at the coordinate x decreases the healths of all monsters between the coordinates x-D and x+D (inclusive) by A.
There is no way other than bombs to decrease the monster's health.

Silver Fox wins when all the monsters' healths become 0 or below.

Find the minimum number of bombs needed to win.

Constraints

1 \leq N \leq 2 \times 10^5

0 \leq D \leq 10^9

1 \leq A \leq 10^9

0 \leq X_i \leq 10^9

1 \leq H_i \leq 10^9

X_i are distinct.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N D A
X_1 H_1
:
X_N H_N

Output

Print the minimum number of bombs needed to win.

Sample Input 1

3 3 2
1 2
5 4
9 2

Sample Output 1

2

First, let us use a bomb at the coordinate 4 to decrease the first and second monsters' health by 2.

Then, use a bomb at the coordinate 6 to decrease the second and third monsters' health by 2.

Now, all the monsters' healths are 0.
We cannot make all the monsters' health drop to 0 or below with just one bomb.

Sample Input 2

9 4 1
1 5
2 4
3 3
4 2
5 1
6 2
7 3
8 4
9 5

Sample Output 2

5

We should use five bombs at the coordinate 5.

Sample Input 3

3 0 1
300000000 1000000000
100000000 1000000000
200000000 1000000000

Sample Output 3

3000000000

Watch out for overflow.

Solution in Kotlin (1.0.0) (judge verdict: Wrong Answer)

import java.util.*

fun main(args: Array<String>) {
    abc153f()
}

fun abc153f() {
    val (n, length, damage) = readLine()!!.split(' ').map { it.toLong() }
    val xhList = (1..n).map {
        readLine()!!.split(' ').map { it.toLong() }.let { Enemy(it[0], it[1]) }
    }.sortedBy { it.pos }

    var answer = 0L
    var currDamage = 0L
    val blasts = ArrayDeque<Blast>()

    for (i in 0 until n) {
        var (pos, hp) = xhList[i.toInt()]

        while (blasts.isNotEmpty() && blasts.peekFirst().endPos < pos) {
            currDamage -= blasts.poll().totalDamage
        }

        hp -= currDamage

        if (hp > currDamage) {
            val needBomb = (hp + damage - 1) / damage
            answer += needBomb
            currDamage += damage * needBomb
            blasts.add(Blast(pos + length * 2, damage * needBomb))
        }
    }

    println(answer)
}

private data class Enemy(val pos: Long, val hp: Long)
private data class Blast(val endPos: Long, val totalDamage: Long)