// clang-format off
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define stoi stoll
using pii = pair<int,int>;
using vi = vector<int>;
using vvi = vector<vi>;
#define all(c) begin(c), end(c)
#define rall(c) rbegin(c), rend(c)
#define fore(x, c) for(auto &&x : c)
#define rep(i, a, n) for(int i = a, i##len = (int)(n); i < i##len; ++i)
#define rrep(i, a, n) for(int i = (int)(n - 1); i >= a; --i)
#define sz(c) ((int)c.size())
#define contains(c, x) (c.find(x) != end(c))
#define inseg(l, x, r) ((l) <= (x) && (x) < (r))
#define dump(...)
#define pb push_back
#define eb emplace_back
#define _ 0
const signed INF_ = 1001001001; const long long INF = 1001001001001001001LL;
const int DX[9] = {0,1,0,-1,1,1,-1,-1,0}, DY[9] = {-1,0,1,0,-1,1,1,-1,0};
template<class T> ostream& operator<<(ostream &os, const vector<T> &v) {
  for (auto i = begin(v); i != end(v); i++) os<<*i<<(i==end(v)-1?"":" ");return os;}
template<class T> istream& operator>>(istream &is, vector<T> &v) {
  for (auto i = begin(v); i != end(v); i++) is>>*i;return is;}
template<class T,class U> istream& operator>>(istream &is, pair<T,U> &p) {
  is>>p.first>>p.second;return is;}
template<class T, class U> bool chmax(T &a, const U &b){return a<b?a=b,1:0;}
template<class T, class U> bool chmin(T &a, const U &b){return a>b?a=b,1:0;}
template <class T> void psum(T& c) {partial_sum(begin(c), end(c), begin(c));}
template<class T> using heap = priority_queue<T, deque<T>, greater<T>>;
struct before_main_function {
  before_main_function() {
      cin.tie(nullptr); ios::sync_with_stdio(0);
      cout << setprecision(15) << fixed;
  }
} before_main_function;
// clang-format on
//------------------8<------------------------------------8<--------------------

// 1-indexed
struct BIT {
  int size;
  int pow2_less;
  vector<int> data;
  BIT(int n) : size(n + 1), data(n + 1, 0) {
    pow2_less = 1;
    while ((pow2_less << 1) <= size) pow2_less <<= 1;
  }
  void add(int i, int x) {
    while (i < size) {
      data[i] += x;
      i += i & -i;
    }
  }
  int sum(int i) {
    int ret = 0;
    while (i > 0) {
      ret += data[i];
      i -= i & -i;
    }
    return ret;
  }
  // sum(x) >= w となる最小のxを返す
  int lower_bound(int w) {
    if (w <= 0) return 0;
    int x = 0;
    for (int k = pow2_less; k > 0; k >>= 1) {
      if (x + k < size && data[x + k] < w) {
        w -= data[x + k];
        x += k;
      }
    }
    return x + 1;
  }
};
signed main() {
  int N, D, A;
  cin >> N >> D >> A;
  vector<pii> XH(N);
  rep(i, 0, N) {
    int x, h;
    cin >> x >> h;
    XH[i] = {x, h};
  }
  sort(all(XH));
  vi Z;
  rep(i, 0, N) {
    Z.pb(XH[i].first);
    Z.pb(XH[i].first + 2 * D);
  }
  sort(all(Z));
  Z.erase(unique(all(Z)), end(Z));
  auto get_idx = [&](int x) { return lower_bound(all(Z), x) - begin(Z); };

  BIT bit((N + 1) * 3);
  int ans = 0;
  rep(i, 0, N) {
    int l = get_idx(XH[i].first);
    int r = get_idx(XH[i].first + 2 * D);
    int cnt = bit.sum(l + 1);
    int h = XH[i].second - cnt * A;
    if (h <= 0) continue;
    int x = (h + A - 1) / A;
    ans += x;
    bit.add(l + 1, x);
    bit.add(r + 2, -x);
  }
  cout << ans << endl;
  return (0 ^ _ ^ 0);
}



Measured memory_bytes: 11756