#!usr/bin/env python3

from collections import defaultdict,deque

from heapq import heappush, heappop

from itertools import permutations

import sys

import math

import bisect

def LI(): return [int(x) for x in sys.stdin.readline().split()]

def I(): return int(sys.stdin.readline())

def LS():return [list(x) for x in sys.stdin.readline().split()]

def S():

    res = list(sys.stdin.readline())

    if res[-1] == "\n":

        return res[:-1]

    return res

def IR(n):

    return [I() for i in range(n)]

def LIR(n):

    return [LI() for i in range(n)]

def SR(n):

    return [S() for i in range(n)]

def LSR(n):

    return [LS() for i in range(n)]



sys.setrecursionlimit(1000000)

mod = 1000000007



def solve():

    def add(i,s):

        while i <= n:

            bit[i] += s

            i += i&-i



    def sum(i):

        res = 0

        while i > 0:

            res += bit[i]

            i -= i&-i

        return res



    n,d,a = LI()

    p = LIR(n)

    bit = [0]*(n+1)

    p.sort()

    ans = 0

    X = [p[i][0] for i in range(n)]

    for i in range(n):

        x,h = p[i]

        j = bisect.bisect_left(X,x-2*d)

        if i != j:

            su = sum(i+1)

            if j > 0:

                su -= sum(j)

            h -=  su

        if h > 0:

            l = x

            k = math.ceil(h/a)

            ans += k

            add(i+1,k*a)

    print(ans)

    return



#Solve

if __name__ == "__main__":

    solve()

#!usr/bin/env python3

from collections import defaultdict,deque

from heapq import heappush, heappop

from itertools import permutations

import sys

import math

import bisect

def LI(): return [int(x) for x in sys.stdin.readline().split()]

def I(): return int(sys.stdin.readline())

def LS():return [list(x) for x in sys.stdin.readline().split()]

def S():

    res = list(sys.stdin.readline())

    if res[-1] == "\n":

        return res[:-1]

    return res

def IR(n):

    return [I() for i in range(n)]

def LIR(n):

    return [LI() for i in range(n)]

def SR(n):

    return [S() for i in range(n)]

def LSR(n):

    return [LS() for i in range(n)]



sys.setrecursionlimit(1000000)

mod = 1000000007



def solve():

    n,d,a = LI()

    p = LIR(n)

    s = [0]*(n+1)

    p.sort()

    ans = 0

    X = [p[i][0] for i in range(n)]

    for i in range(n):

        x,h = p[i]

        j = bisect.bisect_left(X,x-2*d)

        if i != j:

            su = s[i-1]

            if j > 0:

                su -= s[j-1]

            h -=  su

        if h > 0:

            l = x

            k = math.ceil(h/a)

            ans += k

            s[i] = k*a

        s[i] += s[i-1]

    print(ans)

    return



#Solve

if __name__ == "__main__":

    solve()

#!usr/bin/env python3
from collections import defaultdict, deque
from heapq import heappush, heappop
from itertools import permutations
import sys
import math
import bisect


def LI():
    return [int(x) for x in sys.stdin.readline().split()]


def I():
    return int(sys.stdin.readline())


def LS():
    return [list(x) for x in sys.stdin.readline().split()]


def S():
    res = list(sys.stdin.readline())
    if res[-1] == "\n":
        return res[:-1]
    return res


def IR(n):
    return [I() for i in range(n)]


def LIR(n):
    return [LI() for i in range(n)]


def SR(n):
    return [S() for i in range(n)]


def LSR(n):
    return [LS() for i in range(n)]


sys.setrecursionlimit(1000000)
mod = 1000000007


def solve():
    def add(i, s):
        while i <= n:
            bit[i] += s
            i += i & -i

    def sum(i):
        res = 0
        while i > 0:
            res += bit[i]
            i -= i & -i
        return res

    n, d, a = LI()
    p = LIR(n)
    bit = [0] * (n + 1)
    p.sort()
    ans = 0
    X = [p[i][0] for i in range(n)]
    for i in range(n):
        x, h = p[i]
        j = bisect.bisect_left(X, x - 2 * d)
        if i != j:
            su = sum(i + 1)
            if j > 0:
                su -= sum(j)
            h -= su
        if h > 0:
            l = x
            k = math.ceil(h / a)
            ans += k
            add(i + 1, k * a)
    print(ans)
    return


# Solve
if __name__ == "__main__":
    solve()

#!usr/bin/env python3
from collections import defaultdict, deque
from heapq import heappush, heappop
from itertools import permutations
import sys
import math
import bisect


def LI():
    return [int(x) for x in sys.stdin.readline().split()]


def I():
    return int(sys.stdin.readline())


def LS():
    return [list(x) for x in sys.stdin.readline().split()]


def S():
    res = list(sys.stdin.readline())
    if res[-1] == "\n":
        return res[:-1]
    return res


def IR(n):
    return [I() for i in range(n)]


def LIR(n):
    return [LI() for i in range(n)]


def SR(n):
    return [S() for i in range(n)]


def LSR(n):
    return [LS() for i in range(n)]


sys.setrecursionlimit(1000000)
mod = 1000000007


def solve():
    n, d, a = LI()
    p = LIR(n)
    s = [0] * (n + 1)
    p.sort()
    ans = 0
    X = [p[i][0] for i in range(n)]
    for i in range(n):
        x, h = p[i]
        j = bisect.bisect_left(X, x - 2 * d)
        if i != j:
            su = s[i - 1]
            if j > 0:
                su -= s[j - 1]
            h -= su
        if h > 0:
            l = x
            k = math.ceil(h / a)
            ans += k
            s[i] = k * a
        s[i] += s[i - 1]
    print(ans)
    return


# Solve
if __name__ == "__main__":
    solve()

-    def add(i, s): -        while i <= n: -            bit[i] += s -            i += i & -i - -    def sum(i): -        res = 0 -        while i > 0: -            res += bit[i] -            i -= i & -i -        return res - -    bit = [0] * (n + 1) +    s = [0] * (n + 1) -            su = sum(i + 1) +            su = s[i - 1] -                su -= sum(j) +                su -= s[j - 1] -            add(i + 1, k * a) +            s[i] = k * a +        s[i] += s[i - 1]