#include<bits/stdc++.h>
using namespace std;
int n,k,a,b,sum;
struct P{
int h,x;
}p[5005];
bool cmp(P a,P b){
return a.x<b.x;
}
int main(){
cin>>n>>k;
cin>>a>>b;
a=a+b;
for(int i=1;i<=n;i++){
cin>>p[i].h>>p[i].x;
}
sort(p+1,p+n+1,cmp);
for(int i=1;i<=n;i++){
if(p[i].h<=a&&p[i].x<=k){
sum++;
k-=p[i].x;
}
}
cout<<sum;
return 0;
}