#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,s,a,b,h[5001],l[5001],z,i,p=0,zh=0;
	cin>>n>>s>>a>>b;
	z=a+b;
	for(i=1;i<=n;i++)
	{
		cin>>h[i]>>l[i];
		if(h[i]>z) i-=1,n-=1;
	}
		sort(l+1,l+n+1);
	for(int j=1;j<=n;j++,p++)
	{
		zh=zh+l[j];
		if(zh>=s)  break;
	}
	cout<<p;
}