#include<bits/stdc++.h>
using namespace std;
int n,x,y,s,a[5005],b[5005],sum;
void quick_sort(int a[],int b[]){
	for(int i=1;i<n;i++){
		if(a[i]>a[i+1])
			swap(a[i],a[i+1]);
			swap(b[i],b[i+1]);
	}
}
int main(){
	cin>>n>>s>>x>>y;
	for(int i=1;i<=n;i++){
		cin>>a[i]>>b[i];
	}
	quick_sort(b,a);
	for(int i=1;i<=n,s>0;i++){
		if(x+y>=a[i]&&s-b[i]>=0){
			s-=b[i];
			sum++;
		}
	}
	cout<<sum;
	return 0;
}