#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; }

struct Monster {
  i64 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() {
  i64 n, d, a;
  cin >> n >> d >> a;
  vector<Monster> mon;
  rep(i, n) {
    i64 x, h;
    cin >> x >> h;
    mon.push_back({x, h});
  }
  sort(all(mon));
  queue<pair<i64, i64>> q;
  i64 ans = 0;
  i64 tmp = 0;
  rep(i, n) {
    while (q.size()) {
      i64 x, k;
      tie(x, k) = q.front();
      if (x + d * 2 >= mon[i].x) break;
      q.pop();
      tmp -= k;
    }
    i64 rest = max(0ll, mon[i].h - tmp * a);
    i64 c = (rest + a - 1) / a;
    ans += c;
    tmp += c;
    q.emplace(mon[i].x, c);
  }
  cout << ans << endl;
}


Measured memory_bytes: 7660