# Original solution
# -*- coding: utf-8 -*-

import sys
from bisect import bisect_right

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(eval(input()))
def MAP(): return list(map(int, input().split()))
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 18
MOD = 10 ** 9 + 7

class StarrySkyTree:
    """ Starry Sky Tree(区間加算・区間最小(大)値取得) """

    def __init__(self, N, func, intv):
        self.intv = intv
        self.func = func
        LV = (N-1).bit_length()
        self.N0 = 2**LV
        self.data = [0]*(2*self.N0)
        self.lazy = [0]*(2*self.N0)

    # 伝搬される区間のインデックス(1-indexed)を全て列挙するgenerator
    def gindex(self, l, r):
        L = l + self.N0; R = r + self.N0
        lm = (L // (L & -L)) >> 1
        rm = (R // (R & -R)) >> 1
        while L < R:
            if R <= rm:
                yield R
            if L <= lm:
                yield L
            L >>= 1; R >>= 1
        while L:
            yield L
            L >>= 1

    # 遅延評価の伝搬処理
    def propagates(self, *ids):
        # 1-indexedで単調増加のインデックスリスト
        for i in reversed(ids):
            v = self.lazy[i-1]
            if not v:
                continue
            self.lazy[2*i-1] += v; self.lazy[2*i] += v
            self.data[2*i-1] += v; self.data[2*i] += v
            self.lazy[i-1] = 0

    def update(self, l, r, x):
        """ 区間[l,r)の値にxを加算 """

        # 1. lazyの値は伝搬させない
        # 2. 区間[l,r)のdata, lazyの値を更新
        L = self.N0 + l; R = self.N0 + r
        while L < R:
            if R & 1:
                R -= 1
                self.lazy[R-1] += x; self.data[R-1] += x
            if L & 1:
                self.lazy[L-1] += x; self.data[L-1] += x
                L += 1
            L >>= 1; R >>= 1
        # 3. 更新される区間を部分的に含んだ区間のdataの値を更新 (lazyの値を考慮)
        for i in self.gindex(l, r):
            self.data[i-1] = self.func(self.data[2*i-1], self.data[2*i]) + self.lazy[i-1]

    def query(self, l, r):
        """ 区間[l,r)の最小(大)値を取得 """

        # 1. トップダウンにlazyの値を伝搬
        self.propagates(*self.gindex(l, r))
        L = self.N0 + l; R = self.N0 + r

        # 2. 区間[l, r)の最小(大)値を求める
        s = self.intv
        while L < R:
            if R & 1:
                R -= 1
                s = self.func(s, self.data[R-1])
            if L & 1:
                s = self.func(s, self.data[L-1])
                L += 1
            L >>= 1; R >>= 1
        return s

N, D, K = MAP()

XH = []
for i in range(N):
    x, h = MAP()
    XH.append((x, h))

XH.sort()
X, H = list(zip(*XH))
D = D * 2

sst = StarrySkyTree(N+1, max, 0)
ans = 0
for i, (x, h) in enumerate(XH):
    h -= sst.query(i, i+1) * K
    if h <= 0:
        continue
    cnt = ceil(h, K)
    idx = bisect_right(X, x+D) - 1
    sst.update(i, idx+1, cnt)
    ans += cnt
print(ans)


# Optimized solution
# -*- coding: utf-8 -*-

import sys
from bisect import bisect_right

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(eval(input()))
def MAP(): return list(map(int, input().split()))
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 18
MOD = 10 ** 9 + 7

class StarrySkyTree:
    """ Starry Sky Tree(区間加算・区間最小(大)値取得) """

    def __init__(self, N, func, intv):
        self.intv = intv
        self.func = func
        LV = (N-1).bit_length()
        self.N0 = 2**LV
        self.data = [0]*(2*self.N0)
        self.lazy = [0]*(2*self.N0)

    # 伝搬される区間のインデックス(1-indexed)を全て列挙するgenerator
    def gindex(self, l, r):
        L = l + self.N0; R = r + self.N0
        lm = (L // (L & -L)) >> 1
        rm = (R // (R & -R)) >> 1
        while L < R:
            if R <= rm:
                yield R
            if L <= lm:
                yield L
            L >>= 1; R >>= 1
        while L:
            yield L
            L >>= 1

    # 遅延評価の伝搬処理
    def propagates(self, *ids):
        # 1-indexedで単調増加のインデックスリスト
        for i in reversed(ids):
            v = self.lazy[i-1]
            if not v:
                continue
            self.lazy[2*i-1] += v; self.lazy[2*i] += v
            self.data[2*i-1] += v; self.data[2*i] += v
            self.lazy[i-1] = 0

    def update(self, l, r, x):
        """ 区間[l,r)の値にxを加算 """

        # 1. lazyの値は伝搬させない
        # 2. 区間[l,r)のdata, lazyの値を更新
        L = self.N0 + l; R = self.N0 + r
        while L < R:
            if R & 1:
                R -= 1
                self.lazy[R-1] += x; self.data[R-1] += x
            if L & 1:
                self.lazy[L-1] += x; self.data[L-1] += x
                L += 1
            L >>= 1; R >>= 1
        # 3. 更新される区間を部分的に含んだ区間のdataの値を更新 (lazyの値を考慮)
        for i in self.gindex(l, r):
            self.data[i-1] = self.func(self.data[2*i-1], self.data[2*i]) + self.lazy[i-1]

    def query(self, l, r):
        """ 区間[l,r)の最小(大)値を取得 """

        # 1. トップダウンにlazyの値を伝搬
        self.propagates(*self.gindex(l, r))
        L = self.N0 + l; R = self.N0 + r

        # 2. 区間[l, r)の最小(大)値を求める
        s = self.intv
        while L < R:
            if R & 1:
                R -= 1
                s = self.func(s, self.data[R-1])
            if L & 1:
                s = self.func(s, self.data[L-1])
                L += 1
            L >>= 1; R >>= 1
        return s

N, D, K = MAP()

XH = []
for i in range(N):
    x, h = MAP()
    XH.append((x, h))

XH.sort()
X, H = list(zip(*XH))
D = D * 2

sst = StarrySkyTree(N, max, 0)
ans = 0
for i, (x, h) in enumerate(XH):
    h -= sst.query(i, i+1) * K
    if h <= 0:
        continue
    cnt = ceil(h, K)
    idx = bisect_right(X, x+D) - 1
    sst.update(i, idx+1, cnt)
    ans += cnt
print(ans)