#include<bits/stdc++.h>
using namespace std;
struct apple{
	int c,d;
}p[5050];
bool hh(apple x,apple y){
	return x.d<y.d;
}
int main(){
	int n,s,a,b;
	cin>>n>>s;
	cin>>a>>b;
	int can=0;
	for(int i=0;i<n;i++){
		int l,k;
		cin>>l>>k;
		if(l<=a+b){
			
			p[can].c=l;
			p[can].d=k;
			
			can+=1;
		}
	}
	
	sort(p,p+can,hh);
	
	int j=0,sum=0;
	while(s>=0){
		j+=1;
		sum+=1;
		s-=p[j].d;
	}
	cout<<sum<<endl;
	
	
	
}