#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
	int n,s,a,b;
	cin>>n>>s;
	cin>>a>>b;
	int x[1001000],y[1001000];
	for(int i=1;i<=n;i++)    cin>>x[i]>>y[i];
	//sort(x,x+1+n);
	sort(y,y+1+n);
	int sum=0;
	for(int i=1;i<=n;i++)
	{
		if (s>=y[i])
		{
		    if (x[i]<=(a+b))
			{
				sum++;
				s-=y[i];
			} 
			else  continue;	 
		}
		else  break;
	}
	cout<<sum<<endl;
	return 0;
}