#include<bits/stdc++.h>
using namespace std;
struct apple{
	int high,liqi;
}A[5100];
bool cmp(apple a,apple b)
{
	return a.liqi<=b.liqi;
}
int main()
{
	int n,s,a,b,x,y,q=0;
	scanf("%d%d%d%d",&n,&s,&a,&b);
	for(int i=0;i<n;i++)
	{
		scanf("%d%d",&x,&y);
		if(x<=a+b)
		{
			A[q].high=x;
			A[q].liqi=y;
			q++;
		}
	}
	sort(A,A+q,cmp);
	int ans=0;
	for(int i=0;i<q;i++)
	{
		s-=A[i].liqi;
		if(s<0)
		{
			break;
		}
		ans++;
	}
	cout<<ans;
}