# Original solution
# -*- 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]

    ans = 0
    for i in range(N):
        if H[i] <= 0:
            continue
        x = X[i]
        h = H[i]
        n = -(-h // A)
        ans += n
        r = bisect.bisect_right(X, x+2*D)
        for j in range(i, min(r, N)):
            H[j] -= n*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()


# Optimized solution
# -*- 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 i in range(N):
        while q and q[0][0] < X[i]:
            _, d = q.popleft()
            dmg -= d
        if H[i] <= dmg:
            continue
        ans += -(-(H[i] - dmg) // A)
        q.append((X[i]+2*D, (-(-(H[i] - dmg) // A))*A))
        dmg += (-(-(H[i] - 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()