#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

int main() {
    int n,s,a,b,i,j;//n,num s,liqi a,yizi b,zuida
    int xi[5010],yi[5010];
    memset(xi,0,sizeof(xi));
    memset(yi,0,sizeof(yi));
    scanf("%d%d%d%d",&n,&s,&a,&b);
    int maxn=a+b;
    for(i=1; i<=n; i++)
        cin>>xi[i]>>yi[i];
    int total=0;
    for(i=1; i<=n; i++) {
        for(j=1; j<=n; j++) {
            if(yi[i]>yi[i+1]) {
                swap(xi[i],xi[i+1]);
                swap(yi[i],yi[i+1]);
            }
        }
    }
    for(i=1; i<=n; i++) {
        if(maxn>=xi[i]&&s>=yi[i]) {
            s-=yi[i];
            total++;
            continue;
        }
        if(s<yi[i]) {
            break;
        }
    }
    cout<<total;
    return 0;
}