#include <bits/stdc++.h>
using namespace std;
int n,x;
int chair,arm;
int ans = 0;
struct tt{
	int gd;
	int shlq;
}aple[10000];
bool cmp(tt a,tt b){
	a.gd < b.gd && a.shlq < b.shlq;
}
int main(){
	cin >> n >> x;
	cin >> arm >> chair;
	for(int i = 1;i <= n;i++){
		cin >> aple[i].gd >> aple[i].shlq;
	}
	sort(aple + 1,aple + n + 1,cmp);
	for(int i = 1;i <= n;i++){
		if(arm + chair >= aple[i].gd && x >= aple[i].shlq){
			ans++;
			x -= aple[i].shlq;
		}
	}
	cout << ans;
	return 0;
}