#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define each(x, y) for (auto &x : y)
#define all(a) (a).begin(), (a).end()
#define bit(b) (1ll << (b))

using namespace std;

using i32 = int;
using i64 = long long;
using u64 = unsigned long long;
using f80 = long double;
using vi32 = vector<i32>;
using vi64 = vector<i64>;
using vu64 = vector<u64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

inline void yes() { cout << "Yes" << '\n'; exit(0); }
inline void no() { cout << "No" << '\n'; exit(0); }
inline i64 gcd(i64 a, i64 b) { if (min(a, b) == 0) return max(a, b); if (a % b == 0) return b; return gcd(b, a % b); }
inline i64 lcm(i64 a, i64 b) { return a / gcd(a, b) * b; }
inline u64 xorshift() { static u64 x = 88172645463325252ull; x = x ^ (x << 7); return x = x ^ (x >> 9); }
template <typename T> class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T> class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> inline void amax(T &x, T y) { if (x < y) x = y; }
template <typename T> inline void amin(T &x, T y) { if (x > y) x = y; }
template <typename T> inline T exp(T x, i64 n, T e = 1) { T r = e; while (n > 0) { if (n & 1) r *= x; x *= x; n >>= 1; } return r; }
template <typename T> inline T bis(T ok, T ng, function<bool(T)> f, T eps = 1) { while (abs(ok - ng) > eps) { T mi = (ok + ng) / 2; (f(mi) ? ok : ng) = mi; } return ok; }
template <typename T> istream& operator>>(istream &is, vector<T> &v) { each(x, v) is >> x; return is; }
template <typename T> ostream& operator<<(ostream &os, vector<T> &v) { rep(i, v.size()) { if (i) os << ' '; os << v[i]; } return os; }
template <typename T, typename S> istream& operator>>(istream &is, pair<T, S> &p) { is >> p.first >> p.second; return is; }
template <typename T, typename S> ostream& operator<<(ostream &os, pair<T, S> &p) { os << p.first << ' ' << p.second; return os; }
void solve(); int main() { ios::sync_with_stdio(0); cin.tie(0); cout << fixed << setprecision(16); solve(); return 0; }

template <typename T, typename S>
struct LazySegmentTree {
  using F = function<T(T, T)>;
  using G = function<T(T, S, int)>;
  using H = function<S(S, S)>;

  vector<T> v;
  vector<S> z;
  F f;
  G g;
  H h;
  T e;
  S d;
  int n;

  LazySegmentTree(int size, F f, G g, H h, T e, S d) : f(f), g(g), h(h), e(e), d(d) {
    n = 1;
    while (n < size) n <<= 1;
    v.resize(n * 2, e);
    z.resize(n * 2, d);
  }
  
  void set(int k, T x) {
    v[k + n] = x;
  }

  void build() {
    rrep(i, n) v[i] = f(v[i * 2 + 0], v[i * 2 + 1]);
  }

  void propagate(int k, int l, int r) {
    v[k] = g(v[k], z[k], r - l);
    if (k < n) {
      z[k * 2 + 0] = h(z[k * 2 + 0], z[k]);
      z[k * 2 + 1] = h(z[k * 2 + 1], z[k]);
    }
    z[k] = d;
  }

  T update(int a, int b, S x, int k = 1, int l = 0, int r = -1) {
    if (r == -1) r = n;
    propagate(k, l, r);
    if (b <= l || r <= a) return v[k];
    if (a <= l && r <= b) { z[k] = x; propagate(k, l, r); return v[k]; }
    return v[k] = f(
      update(a, b, x, k * 2 + 0, l, (l + r) / 2),
      update(a, b, x, k * 2 + 1, (l + r) / 2, r)
    );
  }

  T query(int a, int b, int k = 1, int l = 0, int r = -1) {
    if (r == -1) r = n;
    propagate(k, l, r);
    if (b <= l || r <= a) return e;
    if (a <= l && r <= b) return v[k];
    return f(
      query(a, b, k * 2 + 0, l, (l + r) / 2),
      query(a, b, k * 2 + 1, (l + r) / 2, r)
    );
  }

  int search(int k = 1, int l = 0, int r = -1) {
    if (r == -1) r = n;
    propagate(k, l, r);
    if (v[k] <= 0) return -1;
    if (r - l == 1) return l;
    int x = search(k * 2 + 0, l, (l + r) / 2);
    if (x != -1) return x;
    return search(k * 2 + 1, (l + r) / 2, r);
  }
};

struct Monster {
  int x, h;
  bool operator<(const Monster &that) const {
    #define lt(x) if (x != that.x) return x < that.x;
    #define gt(x) if (x != that.x) return x > that.x;
    lt(x) lt(h)
    #undef gt
    #undef lt
    return false;
  }
  bool operator>(const Monster &that) const {
    return that < *this;
  }
};

void solve() {
  int n, d, a;
  cin >> n >> d >> a;
  vector<Monster> monsters;
  rep(i, n) {
    int x, h;
    cin >> x >> h;
    monsters.push_back({x, h});
  }
  sort(all(monsters));
  LazySegmentTree<int, int> lst(n,
    [](int a, int b) { return max(a, b); },
    [](int a, int b, int x) { return a + b; },
    [](int a, int b) { return a + b; },
    -1e9, 0);
  rep(i, n) {
    lst.set(i, monsters[i].h);
  }
  lst.build();
  i64 ans = 0;
  while (lst.query(0, n) > 0) {
    int x = lst.search();
    if (x == -1) break;
    i64 ma = (i64) monsters[x].x + (i64) d * 2;
    int y = bis<int>(x, n, [&](int m) { return monsters[m].x <= ma; });
    int h = lst.query(x, x + 1);
    // h <= c * a
    // c * a >= h
    // c >= h / a
    // c = (h + a - 1) / a
    int c = (h + a - 1) / a;
    lst.update(x, y + 1, -a * c);
    ans += c;
  }
  cout << ans << endl;
}


Measured memory_bytes: 6000