#include<bits/stdc++.h>
using namespace std;
int n,s;
struct apple{
	int h,lq;
}arr[5050];
bool cmp1(apple x,apple y){
	return x.h<y.h;
}
bool cmp2(apple x,apple y){
	return x.lq<y.lq;
}
int main(){
//	freopen("P1478.in","r",stdin);
//	freopen("P1478.out","w",stdout);
int a,b;
cin>>n>>s;
cin>>a>>b;
int h1=a+b;
for(int i=1;i<=n;i++){
	cin>>arr[i].h>>arr[i].lq;
}
sort(arr+1,arr+1+n,cmp1);
int k=0,k1=0;
while(arr[k+1].h<=h1){
	k++;
}
sort(arr+1,arr+1+k,cmp2);
while(s>=arr[k1+1].lq&&k1+1<=k){
	k1++;
	s-=arr[k1].lq;
}
cout<<k1;
//	fclose(stdin);
//	fclose(stdout);
	return 0;
}