#include<bits/stdc++.h>
using namespace std;
int cnt;

struct taotao
{
	int high,strength;
}a[5005];

bool cmp(taotao a,taotao b)
{
	if(a.strength<b.strength)
	{
		return true;
	}
	return false;
}

int main()
{
	int n,s,a,b,i;
	cin>>n>>s>>a>>b;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i].high >>a[i].strength;
	}
	sort(a+1,a+1+n,cmp);
	for(int i=1;i<=n;i++)
	{
		if(a[i].high<=a+b)
		{
			cnt++;
			s=s-a[i].strength;
		}
	}
	cout<<cnt;
	return 0;
}