#include<iostream>
#include<algorithm>
using namespace std;
struct pinguo
{
    int m,n;
}a[5005];
bool comp(pinguo a,pinguo b){
    return a.n>b.n;
}
int main()
{
    int shu,li,yizi,shou,x=0;
    cin>>shu>>li>>yizi>>shou;
    for(int i=0;i<shu;i++)cin>>a[i].m>>a[i].n;
    sort(a,a+1,comp);
    for(int i=0;i<shu;i++)
        if(li>=a[i].n && yizi+shou>=a[i].m){
            x++;
            li-=a[i].n;
        }
    cout<<x;
    return 0;
}