#include<bits/stdc++.h>
#define int long long
using namespace std;
struct apple {
	int s, h;
} ap[5010];
int n, s, a, b, ans;
bool cmp(apple a, apple b) {
	return a.s < b.s;
}
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin >> n >> s >> a >> b;
	a += b;
	for (int i = 1; i <= n; i++)cin >> ap[i].h >> ap[i].s;
	sort(ap + 1, ap + n + 1, cmp);
	for (int i = 1; i <= n; i++) {
		if (s < 0)break;
		if (a >= ap[i].h)s -= ap[i].s, ans++;
	}
	cout << max(0ll, ans - 1);
	return 0;
}