#include<bits/stdc++.h>
#define  ll long long
using namespace std;
int n,s,a,b,li[5010],qi[5010];
bool cmp(int x,int y){
	if(x>y) return x>y;
}
int main(){
//	freopen("taotao.in","r",stdin);
//	freopen("taotao.out","w",stdout);
	cin>>n>>s>>a>>b;
	for(int i=1;i<=n;i++) cin>>li[i]>>qi[i];
	int t=a+b,c=1,sum=0,bb=1;
	for(int i=1;i<=n;i++){
		if(t>=li[i]) li[c]=li[i],qi[c]=qi[i];
		c++;
	} 
	sort(qi,qi+n+1,cmp);
	while(sum<=s){
		sum+=qi[bb];
		bb++;
	} 
	cout<<bb-1;
	return 0;
}