#include<bits/stdc++.h>
using namespace std;
struct taap{
	int h=0,l=0;
};
taap a[50005];
bool cmp(taap q,taap p)
{
	return q.l<p.l;
}
int main()
{
	int n,s,a,b,ans=0;
	scanf("%d%d%d%d",&n,&s,&a,&b);
	for(int i=1;i<=n;++i)
		scanf("%d%d",&a[i].h,&a[i].l);
	sort(a+1,a+n+1,cmp);
	int ii=1;
	while(s>=0&&ii<=n)
	{
		ii++;
		if(a[ii].h<=b+a)
			ans++;
	}
	cout<<ans;
	return 0;
}