#include<iostream>
#include<algorithm>

using namespace std;

const int N=6e3;

int n,s;
int a,b;
int f[N];//每个水果消耗的力气

int main()
{
    cin>>n>>s;
    cin>>a>>b;
    
    int cnt=0;
    for(int i=0;i<n;i++)
    {
        int x,y;
        cin>>x>>y;
        if(x<=a+b)f[cnt++]=y;
    }
    
    sort(f,f+cnt);
    
    int ans=0;
    while(s>=0)
    {
        s-=f[ans++];
    }
    cout<<ans-1;
    
    return 0;
}