#include<iostream>
#include<algorithm>
using namespace std;
struct apple
{
	int x,y;
}app[5005];
bool cmp(apple app1,apple app2)
{
	return app1.y<=app2.y;
}
int main()
{
    int n,s,a,b,ans=0;
	cin>>n>>s>>a>>b;
	for(int i=1;i<=n;i++)
	cin>>app[i].x>>app[i].y;
	sort(app+1,app+n+1,cmp);
	for(int i=1;i<=n;i++)
	{
		if(s>=app[i].y)
		{
			if(app[i].x<=b || app[i].x<=b+a)
			{
				ans++;
				s=s-app[i].y;
				if(s<=0)
				break;
			}
		}
	}
	cout<<ans<<endl;
	return 0;
}