#include <iostream>
#include<algorithm>
using namespace std;
typedef struct zsg{
	int h;
	int lq;
	
}zsg;

bool cmp2(zsg a,zsg b){
	return a.lq<b.lq;
}
int main(){
	int n,s,a,b;
	cin>>n>>s;
	cin>>a>>b;
	zsg zb[5005];
	for(int i=0;i<n;i++){
		scanf("%d %d",&zb[i].h,&zb[i].lq);
	}
	sort(zb,zb+n,cmp2);
	int sum=0;
	int i=0;
	int sum2=0;
	while(sum<=s&&i<n){
		if(zb[i].h<=(a+b)){
		sum2++;
		sum+=zb[i].lq;
		}
		i++;
	}	
	if(sum<s) cout<<sum2;
	if(sum>=s) cout<<sum2-1;
}