#include<bits/stdc++.h>
using namespace std;
const int MAXN=1e6+10;
int num,ans;
struct node{
	int tall,qi;
}apple[10000000];
bool cmp(node a,node b)
{
	if(a.qi==b.qi) return a.tall<b.tall;
	return a.qi<b.qi;
}
int main()
{
	int n,s;
	cin>>n>>s;
	int a,b;
	cin>>a>>b;
	a+=b;
	for (int i=1;i<=n;i++)
	{
		cin>>apple[i].tall>>apple[i].qi;
	}
	sort(apple+1,apple+n,cmp);
	for (int i=1;i<=n;i++)
	{
		if(apple[i].tall>a) continue;
		if(s>=apple[i].qi) 
		{
			s-=apple[i].qi;	
		}
		else 
		{
			break;
		}
		ans++;
	}
	cout<<ans<<endl;
	return 0;
}