#include <bits/stdc++.h>
using namespace std;
struct node{
	int x,y;
}tr[5005];
bool cmp(node a,node b){
	return a.y<b.y;
}
int main() {
    int n,s,a,b,cnt=0;
    cin>>n>>s>>a>>b;
    for(int i=1;i<=n;i++){
    	cin>>tr[i].x>>tr[i].y;
	}
	sort(tr+1,tr+n+1,cmp);
	for(int i=1;i<=n&&s>=0;i++){
		if(a+b>=tr[i].x){
			cnt++;
			s-=tr[i].y;
		}
	}
	cout<<cnt;
    return 0;
}