# -*- coding: utf-8 -*-

import bisect

import heapq

import math

import random

import sys

from collections import Counter, defaultdict, deque

from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal

from functools import lru_cache, reduce

from itertools import combinations, combinations_with_replacement, product, permutations

from operator import add, mul, sub



sys.setrecursionlimit(100000)

input = sys.stdin.readline

INF = 2**62-1



def read_int():

    return int(input())





def read_int_n():

    return list(map(int, input().split()))





def read_float():

    return float(input())





def read_float_n():

    return list(map(float, input().split()))





def read_str():

    return input().strip()





def read_str_n():

    return list(map(str, input().split()))





def error_print(*args):

    print(*args, file=sys.stderr)





def mt(f):

    import time



    def wrap(*args, **kwargs):

        s = time.time()

        ret = f(*args, **kwargs)

        e = time.time()



        error_print(e - s, 'sec')

        return ret



    return wrap





@mt

def slv(N, D, A, XH):

    XH.sort()

    X = [x for x, _ in XH]

    H = [h for _, h in XH]



    q = deque()

    ans = 0

    dmg = 0

    for x, h in XH:

        while q and q[0][0] < x:

            _, d = q.popleft()

            dmg -= d

        if h <= dmg:

            continue

        a = -(-(h - dmg) // A)

        ans += a

        q.append((x+2*D, a*A))

        dmg += a*A

    return ans





def main():

    N, D, A = read_int_n()

    XH = [read_int_n() for _ in range(N)]

    print(slv(N, D, A, XH))





if __name__ == '__main__':

    main()

# -*- coding: utf-8 -*-

import bisect

import heapq

import math

import random

import sys

from collections import Counter, defaultdict, deque

from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal

from functools import lru_cache, reduce

from itertools import combinations, combinations_with_replacement, product, permutations

from operator import add, mul, sub



sys.setrecursionlimit(100000)

input = sys.stdin.readline

INF = 2**62-1



def read_int():

    return int(input())





def read_int_n():

    return list(map(int, input().split()))





def read_float():

    return float(input())





def read_float_n():

    return list(map(float, input().split()))





def read_str():

    return input().strip()





def read_str_n():

    return list(map(str, input().split()))





def error_print(*args):

    print(*args, file=sys.stderr)





def mt(f):

    import time



    def wrap(*args, **kwargs):

        s = time.time()

        ret = f(*args, **kwargs)

        e = time.time()



        error_print(e - s, 'sec')

        return ret



    return wrap





@mt

def slv(N, D, A, XH):

    XH.sort()



    q = deque()

    ans = 0

    dmg = 0

    for x, h in XH:

        while q and q[0][0] < x:

            _, d = q.popleft()

            dmg -= d

        if h <= dmg:

            continue

        a = -(-(h - dmg) // A)

        ans += a

        q.append((x+2*D, a*A))

        dmg += a*A

    return ans





def main():

    N, D, A = read_int_n()

    XH = [read_int_n() for _ in range(N)]

    print(slv(N, D, A, XH))





if __name__ == '__main__':

    main()

# -*- coding: utf-8 -*-
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict, deque
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product, permutations
from operator import add, mul, sub

sys.setrecursionlimit(100000)
input = sys.stdin.readline
INF = 2**62 - 1


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input().strip()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args):
    print(*args, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()
        error_print(e - s, "sec")
        return ret

    return wrap


@mt
def slv(N, D, A, XH):
    XH.sort()
    X = [x for x, _ in XH]
    H = [h for _, h in XH]
    q = deque()
    ans = 0
    dmg = 0
    for x, h in XH:
        while q and q[0][0] < x:
            _, d = q.popleft()
            dmg -= d
        if h <= dmg:
            continue
        a = -(-(h - dmg) // A)
        ans += a
        q.append((x + 2 * D, a * A))
        dmg += a * A
    return ans


def main():
    N, D, A = read_int_n()
    XH = [read_int_n() for _ in range(N)]
    print(slv(N, D, A, XH))


if __name__ == "__main__":
    main()

# -*- coding: utf-8 -*-
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict, deque
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product, permutations
from operator import add, mul, sub

sys.setrecursionlimit(100000)
input = sys.stdin.readline
INF = 2**62 - 1


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input().strip()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args):
    print(*args, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()
        error_print(e - s, "sec")
        return ret

    return wrap


@mt
def slv(N, D, A, XH):
    XH.sort()
    q = deque()
    ans = 0
    dmg = 0
    for x, h in XH:
        while q and q[0][0] < x:
            _, d = q.popleft()
            dmg -= d
        if h <= dmg:
            continue
        a = -(-(h - dmg) // A)
        ans += a
        q.append((x + 2 * D, a * A))
        dmg += a * A
    return ans


def main():
    N, D, A = read_int_n()
    XH = [read_int_n() for _ in range(N)]
    print(slv(N, D, A, XH))


if __name__ == "__main__":
    main()

-    X = [x for x, _ in XH] -    H = [h for _, h in XH]