#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n,s,a,b,x,y,app[5010],cnt;
    cin  >> n >> s;
    cin >> a>>b;
    for(int i = 1;i <= n;i++)
    {
        cin >> x >> y;
        if(a+b>=x)
        {
            app[++cnt]=y;
        }
    }
    sort(app+1,app+1+cnt);
    int sum=0; 
    for(int i = 1;i <= n;i++)
    {
        if(s>=app[i])
        {
            s-=app[i];
            sum++;
        }
        else
        {
            break;
        }
    }
    cout << sum;
}