#include<bits/stdc++.h>
using namespace std;
struct node {
	int x,y;
};
node a[5010];
bool cmp (node m,node v) {
	return m.y<m.y;
}
int main (){
    int n,s,p,b;
    cin>>n>>s>>p>>b;
    for (int i=1;i<=n;i++) {
    	cin>>a[i].x>>a[i].y;
	}
	sort(a+1,a+n+1,cmp);
	int ans=0;
	for (int i=i;i<=n;i++) {
		if (a[i].x<=p+b&&s-a[i].y>=0) {
			ans++;
			s-=a[i].y;
		}
	}
	cout<<ans<<endl;
return 0;
}