#include<bits/stdc++.h>
using namespace std;
int n,s,a,b,x[5001],y[5001],num,h,flag[5001];
int main()
{
	int i;
	cin>>n>>s>>a>>b;
	for(i=1;i<=n;i++)
	cin>>x[i]>>y[i];
	h=a+b;
	for(i=1;i<=n;i++)
	{
	    if(h>=x[i])
	    flag[i]=1;
	}
	sort(y+1,y+n+1);
	  for(i=1;i<=n;i++)
       if(flag[i]==1&&s>=y[i])
	    {
	        s=s-y[i];
	        num++;
	        if(s<0)
	        break;
	    }
	cout<<num<<endl;
	return 0;
}