#include<bits/stdc++.h>
using namespace std;
struct apple{
	int x,y;
}z[5005];
bool cmp_1(apple &a,apple &b)
{
	return a.x<b.x;
}
bool cmp_2(apple &a,apple &b)
{
	return a.y<b.y;
}
int main()
{
	int n,s,a,b,ans=0,t=0;
	cin>>n>>s>>a>>b;
	for(int i=1;i<=n;i++)
		cin>>z[i].x>>z[i].y;
	sort(z+1,z+n+1,cmp_1);
	for(int i=1;i<=n;i++)
	{
		if(z[i].x>a+b)
			break;
		else
			++t;
	}
	sort(z+1,z+t+1,cmp_2);
	for(int i=1;i<=t;i++)
	{
		if(s<0)
			break;
		ans++;
		s-=z[i].y;
	}
	cout<<ans-1;
	return 0;
}