#include<bits/stdc++.h>
using namespace std;
#define MAXN 5000+15
int n,s,a,b,ans=0;
struct app{
	int x;
	int y;
}A[MAXN];
bool cmp(app a,app b)
{
	return a.y<b.y;
}
int main()
{
	cin>>n>>s;
	cin>>a>>b;
	int j=1;
	int taotao=a+b;
	for(int i=1;i<=n;i++)
	{
		cin>>A[i].x;
		cin>>A[i].y;
	}
	sort(A+1,A+n+1,cmp);
	while(s-A[j].y>=0)
	{
		if(A[j].x<=taotao)
		{
			ans++;
			j++;
			s-=A[j].y;
		}
		else
		  j++;
	}
	cout<<ans;
	return 0;
}