#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
using namespace std;

using ll = long long;
using  P = pair<int, int>;

int main() {
	int n; ll d, a;
	cin >> n >> d >> a;
	vector<P>p(n);
	for (int i = 0; i < n; i++) {
		cin >> p[i].first >> p[i].second;
	}
	sort(p.begin(), p.end());
	d = d * 2;
	ll tot = 0;
	queue<pair<ll, ll>>q;
	ll ans = 0;
	for (int i = 0; i < n; i++) {
		ll x = p[i].first;
		ll h = p[i].second;
		while (q.size() && q.front().first < x) {
			tot -= q.front().second;
			q.pop();
		}
		h -= tot;
		if (h > 0) {
			ll num = (h + a - 1) / a;
			ans += num;
			ll damage = num * a;
			tot += damage;
			q.emplace(x + d, damage);
		}
	}
	cout << ans << endl;
	return 0;
}