//#define NDEBUG
#include "bits/stdc++.h"
#include <iostream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <array>
#include <random>
#ifdef _MSC_VER
#include <ppl.h>
//#include <boost/multiprecision/cpp_dec_float.hpp>
//#include <boost/multiprecision/cpp_int.hpp>
//#include <boost/rational.hpp>
//#else
//#include <omp.h>
#endif


using namespace std;

#define DUMPOUT cerr
#define dump(...) DUMPOUT<<"  ";DUMPOUT<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"<<endl;DUMPOUT<<"    ";dump_func(__VA_ARGS__)

using uint = unsigned; using ll = long long; using ull = unsigned long long; using pii = pair<int, int>; using pll = pair<ll, ll>; using pdd = pair<double, double>; using pss = pair<string, string>;
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const pair<_KTy, _Ty>& m) { o << "{" << m.first << ", " << m.second << "}"; return o; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const map<_KTy, _Ty>& m) { if (m.empty()) { o << "{ }"; return o; } o << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const unordered_map<_KTy, _Ty>& m) { if (m.empty()) { o << "{ }"; return o; } o << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const vector<_Ty>& v) { if (v.empty()) { o << "{ }"; return o; } o << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const deque<_Ty>& v) { if (v.empty()) { o << "{ }"; return o; } o << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const set<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } o << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const unordered_set<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } o << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; }	o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const stack<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } stack<_Ty> t(s); o << "{" << t.top(); t.pop(); while (!t.empty()) { o << ", " << t.top(); t.pop(); } o << "}";	return o; }
template <typename _Ty> ostream& operator << (ostream& o, const list<_Ty>& l) { if (l.empty()) { o << "{ }"; return o; } o << "{" << l.front(); for (auto itr = ++l.begin(); itr != l.end(); ++itr) { o << ", " << *itr; } o << "}"; return o; }
template <typename _KTy, typename _Ty> istream& operator >> (istream& is, pair<_KTy, _Ty>& m) { is >> m.first >> m.second; return is; }
template <typename _Ty> istream& operator >> (istream& is, vector<_Ty>& v) { for (size_t t = 0; t < v.size(); t++) is >> v[t]; return is; }
template <typename _Ty> istream& operator >> (istream& is, deque<_Ty>& v) { for (size_t t = 0; t < v.size(); t++) is >> v[t]; return is; }
namespace aux { // print tuple
  template<typename Ty, unsigned N, unsigned L> struct tp { static void print(ostream& os, const Ty& v) { os << get<N>(v) << ", "; tp<Ty, N + 1, L>::print(os, v); } };
  template<typename Ty, unsigned N> struct tp<Ty, N, N> { static void print(ostream& os, const Ty& v) { os << get<N>(v); } };
}

template<typename... Tys> ostream& operator<<(ostream& os, const tuple<Tys...>& t) { os << "{"; aux::tp<tuple<Tys...>, 0, sizeof...(Tys) - 1>::print(os, t); os << "}"; return os; }

template<typename A, size_t N, typename T> inline void Fill(A(&array)[N], const T& val) { fill((T*)array, (T*)(array + N), val); }

void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) { DUMPOUT << head; if (sizeof...(Tail) == 0) { DUMPOUT << " "; } else { DUMPOUT << ", "; } dump_func(move(tail)...); }

#define PI 3.14159265358979323846
#define EPS 1e-8
#define FOR(t,a,n) for(int t=(a);t<(n);++t)
#define REP(t,n)  FOR(t,0,n)
#define all(j) (j).begin(), (j).end()
#define SZ(j) ((int)(j).size())
#define fake false

class Timer {
public:
  double t = 0;
  Timer() {}
  static double time() {
#ifdef _MSC_VER
    return __rdtsc() / 2.8e9;
#else
    unsigned long long a, d;
    __asm__ volatile("rdtsc"
      : "=a"(a), "=d"(d));
    return (d << 32 | a) / 2.8e9;
#endif
  }
  void measure() { t = time() - t; }
  double elapsedMs() { return (time() - t) * 1000.0; }
} timer;

struct Xorshift {
  uint64_t x = 88172645463325252LL;
  unsigned next_int() {
    x = x ^ (x << 7);
    return x = x ^ (x >> 9);
  }
  unsigned next_int(unsigned mod) {
    x = x ^ (x << 7);
    x = x ^ (x >> 9);
    return x % mod;
  }
  unsigned next_int(unsigned l, unsigned r) {
    x = x ^ (x << 7);
    x = x ^ (x >> 9);
    return x % (r - l + 1) + l;
  }
  double next_double() {
    return double(next_int()) / UINT_MAX;
  }
} rnd;

template<typename T>
void shuffle_vector(vector<T>& v, Xorshift& rnd) {
  int n = v.size();
  for (int i = n - 1; i >= 1; i--) {
    int r = rnd.next_int(i);
    swap(v[i], v[r]);
  }
}



template <typename T, typename E>
struct SegmentTree {
  typedef function<T(T, T)> F;
  typedef function<T(T, E)> G;
  typedef function<E(E, E)> H;
  typedef function<E(E, int)> P;
  int n;
  F f;
  G g;
  H h;
  P p;
  T d1;
  E d0;
  vector<T> dat;
  vector<E> laz;
  SegmentTree(int n_, F f, G g, H h, T d1, E d0,
    vector<T> v = vector<T>(), P p = [](E a, int b) {return a; }) :
    f(f), g(g), h(h), d1(d1), d0(d0), p(p) {
    init(n_);
    if (n_ == (int)v.size()) build(n_, v);
  }
  void init(int n_) {
    n = 1;
    while (n < n_) n *= 2;
    dat.clear();
    dat.resize(2 * n - 1, d1);
    laz.clear();
    laz.resize(2 * n - 1, d0);
  }
  void build(int n_, vector<T> v) {
    for (int i = 0; i < n_; i++) dat[i + n - 1] = v[i];
    for (int i = n - 2; i >= 0; i--)
      dat[i] = f(dat[i * 2 + 1], dat[i * 2 + 2]);
  }
  inline void eval(int len, int k) {
    if (laz[k] == d0) return;
    if (k * 2 + 1 < n * 2 - 1) {
      laz[k * 2 + 1] = h(laz[k * 2 + 1], laz[k]);
      laz[k * 2 + 2] = h(laz[k * 2 + 2], laz[k]);
    }
    dat[k] = g(dat[k], p(laz[k], len));
    laz[k] = d0;
  }
  T update(int a, int b, E x, int k, int l, int r) {
    eval(r - l, k);
    if (r <= a || b <= l) return dat[k];
    if (a <= l && r <= b) {
      laz[k] = h(laz[k], x);
      return g(dat[k], p(laz[k], r - l));
    }
    return dat[k] = f(update(a, b, x, k * 2 + 1, l, (l + r) / 2),
      update(a, b, x, k * 2 + 2, (l + r) / 2, r));
  }
  T update(int a, int b, E x) {
    return update(a, b, x, 0, 0, n);
  }
  T query(int a, int b, int k, int l, int r) {
    eval(r - l, k);
    if (r <= a || b <= l) return d1;
    if (a <= l && r <= b) return dat[k];
    T vl = query(a, b, k * 2 + 1, l, (l + r) / 2);
    T vr = query(a, b, k * 2 + 2, (l + r) / 2, r);
    return f(vl, vr);
  }
  T query(int a, int b) {
    return query(a, b, 0, 0, n);
  }
};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N;
  ll D, A;
  cin >> N >> D >> A;
  vector<pll> XH(N);
  cin >> XH;
  sort(all(XH), [&](const pll& a, const pll& b) {
    return a.first < b.first;
  });
  vector<ll> x(N), hp(N);
  REP(i, N) {
    x[i] = XH[i].first;
    hp[i] = XH[i].second;
  }

  // greedy
  ll W = D * 2 + 1;
  // [L, R) のモンスターに (e.second + A - 1) / A 回攻撃

  auto g = [](ll a, ll b) { return a + b; };
  auto h = [](ll a, ll b) { return a * b; };
  SegmentTree<ll, ll> seg(N, g, g, g, 0LL, 0LL, hp, h);

  ll ans = 0;
  for (ll i = 0; i < N; i++) {
    ll L = x[i];
    ll R = L + W;
    ll h = seg.query(i, i + 1);
    if (h <= 0) continue;
    ll na = (h + A - 1) / A;
    ans += na;
    // R 未満の最大の座標のインデックス
    ll j = lower_bound(all(x), R) - x.begin();
    seg.update(i, j, -na * A);
  }

  cout << ans << endl;

  return 0;
}


Measured memory_bytes: 17792