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 > 0) {
            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)
