#include<iostream>
#include<iomanip>
#include<cmath>
#include<string>
#include<algorithm>
using namespace std;
struct s{
	int x,y;
}a[5005];
bool cmp(const s &a,s &b){
	if(a.y!=b.y) return a.y<b.y;
}
int main(){
	int sum=0,n,u,w,f;
	cin>>n>>f>>u>>w;
	for(int i=1;i<=n;i++){
		cin>>a[i].x>>a[i].y;
	}
	sort(a+1,a+1+n,cmp);
	int g=0;
	while(f>0){
		g++;
		if(a[g].y<=f&&(u+w)>=a[g].x){
			f-=a[g].y;		
			sum++;				
		}
	}
	cout<<sum<<endl;
	return 0;
}