#include<bits/stdc++.h>
using namespace std;
long long power[1000001],high[10000001];
int main()
{
	long long n,i,a,b,s,w,ss=0;
	cin>>n>>s;
	cin>>a>>b;
	for(i=1;i<=n;i++){
		cin>>high[i]>>power[i];
	}
	w=a+b;
	sort(power+1,power+1+n);
	for(i=1;i<=n;i++){
		if(s<=0){
			break;
		}
		else if(high[i]<=w&&s>0&&s>=power[i]){
			ss++;
		}
		s=s-power[i];
	}
	cout<<ss;
	return 0;
}