#pragma region template
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vld = vector<ld>;
using vvld = vector<vld>;
using vvvld = vector<vvld>;
using vs = vector<string>;
using pll = pair<ll, ll>;
using vp = vector<pll>;
template <typename T>
using pqrev = priority_queue<T, vector<T>, greater<T>>;
#define rep(i, n) for (ll i = 0, i##_end = (n); i < i##_end; i++)
#define repb(i, n) for (ll i = (n)-1; i >= 0; i--)
#define repr(i, a, b) for (ll i = (a), i##_end = (b); i < i##_end; i++)
#define reprb(i, a, b) for (ll i = (b)-1, i##_end = (a); i >= i##_end; i--)
#define ALL(a) (a).begin(), (a).end()
#define SZ(x) ((ll)(x).size())
//*
constexpr ll MOD = 1e9 + 7;
/*/
constexpr ll MOD = 998244353;
//*/
constexpr ll INF = 1e+18;
constexpr ld EPS = 1e-12L;
constexpr ld PI = 3.14159265358979323846L;
constexpr ll GCD(ll a, ll b) { return b ? GCD(b, a % b) : a; }
constexpr ll LCM(ll a, ll b) { return a / GCD(a, b) * b; }
template <typename S, typename T>
inline bool chmax(S &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename S, typename T>
inline bool chmin(S &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
#ifdef OJ_LOCAL
#include "dump.hpp"
#else
#define dump(...) ((void)0)
#endif
template <typename T>
bool print_(const T &a) {
  cout << a;
  return true;
}
template <typename T>
bool print_(const vector<T> &vec) {
  for (auto &a : vec) {
    cout << a;
    if (&a != &vec.back()) {
      cout << " ";
    }
  }
  return false;
}
template <typename T>
bool print_(const vector<vector<T>> &vv) {
  for (auto &v : vv) {
    for (auto &a : v) {
      cout << a;
      if (&a != &v.back()) {
        cout << " ";
      }
    }
    if (&v != &vv.back()) {
      cout << "\n";
    }
  }
  return false;
}
void print() { cout << "\n"; }
template <typename Head, typename... Tail>
void print(Head &&head, Tail &&... tail) {
  bool f = print_(head);
  if (sizeof...(tail) != 0) {
    cout << (f ? " " : "\n");
  }
  print(forward<Tail>(tail)...);
}
#pragma endregion

template <typename T, typename E, typename F, typename G, typename H, typename P>
struct LazySegmentTree {
  int N;
  T T_identity;
  E E_identity;
  F merge;      // (T, T) -> T
  G operate;    // (T, E) -> T
  H merge_op;   // (E, E) -> E
  P operate_ex; // (E, int) -> E
  vector<T> node;
  vector<T> lazy;
  LazySegmentTree(F mg, G op, H m_op, P op_ex, T tid, E eid,
      const vector<T> &vec = vector<T>())
      : T_identity(tid), E_identity(eid), merge(mg), operate(op),
        merge_op(m_op), operate_ex(op_ex) {
    build(vec);
  }
  void build(const vector<T> &vec) {
    int sz = vec.size();
    N = 1;
    while (N < sz) {
      N <<= 1;
    }
    node.resize(2 * N - 1, T_identity);
    lazy.resize(2 * N - 1, E_identity);
    for (int i = 0; i < sz; i++) {
      node[i + N - 1] = vec[i];
    }
    for (int i = N - 2; i >= 0; i--) {
      node[i] = merge(node[2 * i + 1], node[2 * i + 2]);
    }
  }
  inline void eval(int len, int k) {
    if (lazy[k] == E_identity) {
      return;
    }
    if (k * 2 + 1 < N * 2 - 1) {
      lazy[k * 2 + 1] = merge_op(lazy[k * 2 + 1], lazy[k]);
      lazy[k * 2 + 2] = merge_op(lazy[k * 2 + 2], lazy[k]);
    }
    node[k] = operate(node[k], operate_ex(lazy[k], len));
    lazy[k] = E_identity;
  }
  T update(int a, int b, E x, int k, int l, int r) {
    eval(r - l, k);
    if (r <= a || b <= l) {
      return node[k];
    }
    if (a <= l && r <= b) {
      lazy[k] = merge_op(lazy[k], x);
      return operate(node[k], operate_ex(lazy[k], r - l));
    }
    return node[k] = merge(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 T_identity;
    }
    if (a <= l && r <= b) {
      return node[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 merge(vl, vr);
  }
  T query(int a, int b) {
    return query(a, b, 0, 0, N);
  }
  T operator[](const int idx) {
    return query(idx, idx+1, 0, 0, N);
  }
};

// F, G, H
auto st_min = [](ll a, ll b) { return min(a, b); };
auto st_max = [](ll a, ll b) { return max(a, b); };
auto st_sum = [](ll a, ll b) { return a + b; };
auto st_upd = [](ll a, ll b) { return b == -INF ? a : b; };
auto st_upd0 = [](ll a, ll b) { return b == 0 ? a : b; };

// P
auto st_mul = [](ll a, ll b) { return a * b; };
auto st_no = [](ll a, ll) { return a; };

/*

// range add / range sum
LazySegmentTree<ll, ll, decltype(st_sum),
  decltype(st_sum), decltype(st_sum), decltype(st_mul)>
seg(st_sum, st_sum, st_sum, st_mul, 0, 0, vll(n, 0));

// range upd / range sum
LazySegmentTree<ll, ll, decltype(st_sum),
  decltype(st_upd), decltype(st_upd), decltype(st_no)>
seg(st_sum, st_upd, st_upd, st_no, 0, 0, vll(n, 0));

// range upd / range min
LazySegmentTree<ll, ll, decltype(st_min),
  decltype(st_upd), decltype(st_upd), decltype(st_no)>
seg(st_min, st_upd, st_upd, st_no, INF, INF, vector<ll>(n, INF));

// range upd / range max
LazySegmentTree<ll, ll, decltype(st_max),
  decltype(st_upd), decltype(st_upd), decltype(st_no)>
seg(st_max, st_upd, st_upd, st_no, -INF, -INF, vector<ll>(n, -INF));

// range add / range min
LazySegmentTree<ll, ll, decltype(st_min),
  decltype(st_sum), decltype(st_sum), decltype(st_no)>
seg(st_min, st_sum, st_sum, st_no, INF, 0, a);

// range upd / range sum
LazySegmentTree<ll, ll, decltype(st_sum),
  decltype(st_upd), decltype(st_upd), decltype(st_mul)>
seg(st_sum, st_upd, st_upd, st_mul, 0, -INF, vector<ll>(n, 0));

*/

// {10, 3, 1, -5, 1} -> {3, 2, 1, 0, 1}
// unzip: {-5, 1, 3, 10}
template <typename T>
vector<T> CoordinateCompression(const vector<T> &x, vector<T> &unzip) {
  int n = x.size();
  vector<T> ret(n);
  unzip = x;
  sort(unzip.begin(), unzip.end());
  unzip.erase(unique(unzip.begin(), unzip.end()), unzip.end());
  for (int i = 0; i < n; i++) {
    ret[i] = lower_bound(unzip.begin(), unzip.end(), x[i]) - unzip.begin();
  }
  return ret;
}

// v1をソートし、v2を対応する位置に移動する
template <typename T, typename U>
void pairSort(vector<T> &v1, vector<U> &v2, bool rev = false) {
  int n = v1.size();
  vector<pair<T, U>> p(n);
  for (int i = 0; i < n; i++) {
    p[i] = pair<T, U>(v1[i], v2[i]);
  }
  if (rev) {
    sort(p.begin(), p.end(), [&](const auto &l, const auto &r) {
      if (l.first == r.first)
        return l.second > r.second;
      else
        return l.first < r.first;
    });
  } else {
    sort(p.begin(), p.end());
  }
  for (int i = 0; i < n; i++) {
    v1[i] = p[i].first;
    v2[i] = p[i].second;
  }
}


int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);
  ll n, d, a;
  cin >> n >> d >> a;
  vll x(n), h(n);
  rep(i, n){
    cin >> x[i] >> h[i];
  }
  pairSort(x, h);
  /*
  vll unzip(n, 0);
  x = CoordinateCompression(x, unzip);
  */
  LazySegmentTree<ll, ll, decltype(st_min),
    decltype(st_sum), decltype(st_sum), decltype(st_no)>
  seg(st_min, st_sum, st_sum, st_no, INF, 0, h);
  ll ans = 0;
  rep(i, n){
    ll j = upper_bound(ALL(x), x[i]+2*d) - x.begin();
    ll q = seg.query(i, i+1);
    if(q > 0){
      ans += (q+a-1)/a;
      seg.update(i, j, -(q+a-1)/a*a);
    }
  }
  print(ans);
}


Measured memory_bytes: 11592