#include <iostream>
#include <algorithm>

using namespace std;
int v[5010];

int main() {
    int n, w, a, b;
    cin >> n >> w;
    cin >> a >> b;

   int cnt = 0;

    for (int i = 0; i < n; i++) {
      int x,y;
      cin>>x>>y;
      if(a+b>=x) v[cnt++] =y;
    }

   sort(v,v+cnt);

   int res =0;
   for(int i =0;i<cnt;i++)
   {
       if(w>=v[i]) 
       {
           w-=v[i];
           res++;
       }
       else break;
   }
    cout<<res<<endl;
    return 0;
}