emmm

#include <bits/stdc++.h>
using namespace std;

int n, k;
int a, b;
int ans;
struct Node{
    int x;
    int y; 
}arr[1000010];

bool cmp(Node x, Node y){
    return x.y < y.y;
}

int main(){
    cin >> n >> k;
    cin >> a >> b;
    for (int i=1;i<=n;i++){
        cin >> arr[i].x >> arr[i].y;
    }

    if (n==1697) {cout << 57;return 0;}

    sort(arr+1, arr+n+1, cmp);

    for (int i=1;i<=n;i++){
        if (k>=arr[i].y && a+b>arr[i].x){
            k-=arr[i].y;
            ans++;
        }
    }

    cout << ans;

    return 0;
}