#include<bits/stdc++.h>
using namespace std;
int n,s,a,b,x,y,can,rest,ans;
struct apple{
    int xi,yi;
}ap[50005];
int cmp(apple x,apple y){
    return x.yi<y.yi;
}
int main(){
	cin>>n>>s>>a>>b;
    for(int i=1;i<=n;i++){
    	cin>>x>>y;
    	if(x<=a+b){
    		can++;
            ap[can].xi=x;
            ap[can].yi=y;	
		}
	}
	sort(ap+1,ap+can+1,cmp);
    rest=s;
    ans=0;
    for(int i=1;rest>=ap[i].yi&&i<=can;i++){
    	ans++;
        rest-=ap[i].yi;
	}
	cout<<ans;
    return 0;
}