#include<bits/stdc++.h>
using namespace std;
int lx[100005];
struct aaa{
	int g;
	int l;
}oye[100005];
bool cmp(struct aaa i,struct aaa j)
{
	return i.l<j.l;
}
int main()
{
	int s=0,n,m,a,b;
	cin>>n>>m>>a>>b;
	for(int i=1;i<=n;i++)
	{
		cin>>oye[i].g>>oye[i].l;
	}
	sort(oye+1,oye+n+1,cmp);
	for(int i=1;i<=n;i++)
	{
		if(oye[i].g<=a+b)lx[s++]=i;
	}
	int s1=1;
	s=0;
	while(m>0)
	{
		if(m-lx[s1]<0)break;
		m-=lx[s1++];
		s++;
	}
	cout<<s;
}