#include<bits/stdc++.h> 
using namespace std;
const int MAXN=5010;
struct Node{
	int height;
	int cost;
}node[MAXN];
bool cmp(Node a,Node b){
	if(a.cost!=b.cost) return a.cost<b.cost;
	else return a.height<b.height;
}
int main()
{
	freopen("in.txt","r",stdin);
	int n,s;cin>>n>>s;
	int a,b;cin>>a>>b;
	for(int i=0;i<n;i++){
		int h,c;cin>>h>>c;
		node[i].cost=c;node[i].height=h;
	}
	sort(node,node+n,cmp);
	int l=a+b;
	int cnt=0;
	for(int i=0;i<n;i++){
		if(s>=node[i].cost&&l>=node[i].height){
			cnt++;s-=node[i].cost;	
		} 
	}
	cout<<cnt;
	return 0;
}