#include<bits/stdc++.h>
using namespace std;
int n,s,a,b,ans=0,t1,t2;
int xi[5010],yi[5010];
int main(){
	cin>>n>>s>>a>>b;
	a+=b;
	for(int i=1;i<=n;i++)
		cin>>xi[i]>>yi[i];
	for(int i=1;i<n;i++)
		for(int j=i+1;j<=n;j++){
			if(yi[i]>yi[j]){
				t1=xi[i],t2=yi[i];
				xi[i]=xi[j],yi[i]=yi[j];
				xi[j]=t1,yi[j]=t2;
			}
		}
	for(int i=1;i<=n;i++){
		if(xi[i]<=a&&yi[i]<=s){
			ans++;
			s-=yi[i];
		}
	}
	cout<<ans;
	return 0;
}