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