def getN():
    return int(input())
def getNM():
    return map(int, input().split())
def getList():
    return list(map(int, input().split()))
def getArray(intn):
    return [int(input()) for i in range(intn)]
def input():
    return sys.stdin.readline().rstrip()
def rand_N(ran1, ran2):
    return random.randint(ran1, ran2)
def rand_List(ran1, ran2, rantime):
    return [random.randint(ran1, ran2) for i in range(rantime)]
def rand_ints_nodup(ran1, ran2, rantime):
  ns = []
  while len(ns) < rantime:
    n = random.randint(ran1, ran2)
    if not n in ns:
      ns.append(n)
  return sorted(ns)

def rand_query(ran1, ran2, rantime):
  r_query = []
  while len(r_query) < rantime:
    n_q = rand_ints_nodup(ran1, ran2, 2)
    if not n_q in r_query:
      r_query.append(n_q)
  return sorted(r_query)

from collections import defaultdict, deque, Counter
from sys import exit
from decimal import *
import heapq
import math
from fractions import gcd
import random
import string
import copy
from itertools import combinations, permutations, product
from operator import mul, itemgetter
from functools import reduce
from bisect import bisect_left, bisect_right

import sys
sys.setrecursionlimit(1000000000)
mod = 10 ** 9 + 7

#############
# Main Code #
#############

#####segfunc#####
def segfunc(x, y):
    return min(x, y)
#################

#####ide_ele#####
ide_ele = 2**31 - 1
#################

class LazySegmentTree:
    """
    init(init_val, ide_ele): 配列init_valで初期化 O(N)
    add(l, r, x): 区間[l, r)にxを加算 O(logN)
    query(l, r): 区間[l, r)をsegfuncしたものを返す O(logN)
    """
    def __init__(self, init_val, segfunc, ide_ele):
        """
        init_val: 配列の初期値
        segfunc: 区間にしたい操作
        ide_ele: 単位元
        num: n以上の最小の2のべき乗
        data: 値配列(1-index)
        lazy: 遅延配列(1-index)
        """
        n = len(init_val)
        self.segfunc = segfunc
        self.ide_ele = ide_ele
        self.num = 1 << (n - 1).bit_length()
        self.data = [ide_ele] * 2 * self.num
        self.lazy = [0] * 2 * self.num
        # 配列の値を葉にセット
        for i in range(n):
            self.data[self.num + i] = init_val[i]
        # 構築していく
        for i in range(self.num - 1, 0, -1):
            self.data[i] = self.segfunc(self.data[2 * i], self.data[2 * i + 1])

    def gindex(self, l, r):
            """
            伝搬する対象の区間を求める
            lm: 伝搬する必要のある最大の左閉区間
            rm: 伝搬する必要のある最大の右開区間
            """
            l += self.num
            r += self.num
            lm = l >> (l & -l).bit_length()
            rm = r >> (r & -r).bit_length()

            while r > l:
                if l <= lm:
                    yield l
                if r <= rm:
                    yield r
                r >>= 1
                l >>= 1
            while l:
                yield l
                l >>= 1

    def propagates(self, *ids):
        """
        遅延伝搬処理
        ids: 伝搬する対象の区間
        """
        for i in reversed(ids):
            v = self.lazy[i]
            if not v:
                continue
            self.lazy[2 * i] += v
            self.lazy[2 * i + 1] += v
            self.data[2 * i] += v
            self.data[2 * i + 1] += v
            self.lazy[i] = 0

    def add(self, l, r, x):
        """
        区間[l, r)の値にxを加算
        l, r: index(0-index)
        x: additional value
        """
        *ids, = self.gindex(l, r)
        l += self.num
        r += self.num
        while l < r:
            if l & 1:
                self.lazy[l] += x
                self.data[l] += x
                l += 1
            if r & 1:
                self.lazy[r - 1] += x
                self.data[r - 1] += x
            r >>= 1
            l >>= 1
        for i in ids:
            self.data[i] = self.segfunc(self.data[2 * i], self.data[2 * i + 1]) + self.lazy[i]


    def query(self, l, r):
        """
        [l, r)のsegfuncしたものを得る
        l: index(0-index)
        r: index(0-index)
        """
        *ids, = self.gindex(l, r)
        self.propagates(*ids)

        res = self.ide_ele

        l += self.num
        r += self.num
        while l < r:
            if l & 1:
                res = self.segfunc(res, self.data[l])
                l += 1
            if r & 1:
                res = self.segfunc(res, self.data[r - 1])
            l >>= 1
            r >>= 1
        return res

def or_less(array, x):
    # arrayの中のx以下のもののインデックス
    # arrayの中のx以下のもののうちの最大値
    index = bisect_right(array, x)
    if index == 0:
        or_less_int = -float('inf')
    else:
        or_less_int = array[index - 1]
    return index - 1

N, D, A = getNM()
que = [getList() for i in range(N)]
que.sort()

HP = [i[1] for i in que]
dis = [i[0] for i in que]

seg = LazySegmentTree([0] * (N + 1), segfunc, ide_ele)
# 現在のインデックス
now = 0
# 現在の場所
now_dis = dis[now]

ans = 0
while now < N:
    # 爆発範囲
    range = or_less(dis, now_dis + 2 * D)
    left_hp = HP[now] - seg.query(now, now + 1)
    # 爆発回数
    explo = (left_hp + A - 1) // A
    seg.add(now, range + 1, explo * A)
    ans += explo

    while True:
        if now >= N or seg.query(now, now + 1) < HP[now]:
            break
        now += 1
    if now < N:
        now_dis = dis[now]

print(ans)

Measured memory_bytes: 152124