#include <bits/stdc++.h>
 
//#include <unistd.h>
//#include <iostream>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl;
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
typedef long long ll;
#define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const long double pi = 3.1415926535897932384626433832795028841971L;
#define Sp(p) cout<<setprecision(25)<< fixed<<p<<endl;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
const ll MOD = 1000000007;
//const ll MOD = 998244353;
// #define mp make_pair
//#define endl '\n'


template <typename T1, typename T2>
class LazySegmentTree {
public:
  using F = function<T1(T1&, T1&)>; // query_func
  using G = function<T2(T2&, T2&)>; // update_func
  using H = function<T1(T1&, T2&, int, int)>; // lazy to node (node, lazy, left, right)
  int n;
  vector<T1> node;
  vector<T2> lazy;
  T1 e1;
  T2 e2;
  F query_func;
  G update_func;
  H eval_func;

  LazySegmentTree(vector<T1> a, F query_func, G update_func, H eval_func, T1 e1, T2 e2)
	:query_func(query_func), update_func(update_func), eval_func(eval_func), e1(e1), e2(e2)
  {
	int _n = a.size();
	n = 1; while (n < _n) n *= 2;
	node.resize(2 * n - 1, e1);
	lazy.resize(2 * n - 1, e2);
	for (int i = 0; i < _n; i++) node[i + n - 1] = a[i];
	for (int i = n - 2; i >= 0; i--) {
	  node[i] = query_func(node[i * 2 + 1], node[i * 2 + 2]);
	}
  }

  // k�Ԗڂ̃m�[�h�ɂ��Ēx���]�����s��
  inline void eval(int k, int l, int r) {
	if (lazy[k] != e2) { // Change
	  node[k] = eval_func(node[k], lazy[k], l, r);
	  if (r - l > 1) {
		lazy[2 * k + 1] = update_func(lazy[2*k + 1], lazy[k]);
		lazy[2 * k + 2] = update_func(lazy[2*k + 2], lazy[k]);
	  }
	  lazy[k] = e2; // Change
	}
  }

  // [a, b)��x�ɂ���
  void update(int a, int b, T2 x, int k, int l, int r) {
	// k �Ԗڂ̃m�[�h�ɑ΂��Ēx���]�����s��
	eval(k, l, r);
	if (b <= l || r <= a) return;
	if (a <= l && r <= b) {
	  lazy[k] = update_func(lazy[k], x);
	  eval(k, l, r);
	}
	else {
	  update(a, b, x, 2 * k + 1, l, (l + r) / 2);
	  update(a, b, x, 2 * k + 2, (l + r) / 2, r);
	  node[k] = query_func(node[2 * k + 1], node[2 * k + 2]);
	}
  }

  T1 query(int a, int b, int k, int l, int r) {
	eval(k, l, r);
	if (b <= l || r <= a) return e1;
	if (a <= l && r <= b) return node[k];
	T1 resl = query(a, b, 2 * k + 1, l, (l + r) / 2);
	T1 resr = query(a, b, 2 * k + 2, (l + r) / 2, r);
	return query_func(resl, resr);
  }
};

ll f(ll a, ll b) {return a + b;}
ll g(ll a, ll b) {return a + b;}
ll hh(ll a, ll b, int l, int r) {return a + b * (r - l);}

signed main() {
	ll n, d, a;
	cin >> n >> d >> a;
	vector<pll> xh(n);
	rep (i, n) {
		cin >> xh[i].first >> xh[i].second;
	}
	sort(all(xh));
	vl x(n), h(n);
	rep (i, n) {
		x[i] = xh[i].first;
		h[i] = xh[i].second;
		if (h[i] % a == 0) h[i] = h[i] / a;
		else h[i] = h[i] / a + 1;
	}

	LazySegmentTree<ll, ll> seg(h, f, g, hh, 0, 0);

	int r = 0;
	ll ans = 0;
	rep (i, n) {
		ll mid_x = x[i] + d;
		while (r < n - 1 and x[r + 1] - mid_x <= d) r++;
		int x = seg.query(i, i + 1, 0, 0, seg.n);
		if (x > 0) {
			seg.update(i, r + 1, -x, 0, 0, seg.n);
			ans += x;
		}
	}
	cout << ans << endl;

}

Measured memory_bytes: 16256