#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

const int N = 5010;

struct Guai
{
    int attack;
    int life;

    bool operator< (const Guai& W)const
    {
        return life < W.life;
    }
}q[N];
int ans;

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

    int A, B;
    cin >> A >> B;

    for (int i = 0; i < n; i++) cin >> q[i].attack >> q[i].life;

    sort(q, q + n);

    for (int i = 0; i < n; i++) 
    {
        if (A + B < q[i].attack) continue;

        if (w - q[i].life < 0) continue;

        w -= q[i].life;
        ans++;

        if (w == 0) break;
    }

    cout << ans << endl;

    return 0;
}