#include<bits/stdc++.h>
using namespace std;
struct m{
	int x,y;
}l[10001];

bool cmp(m c,m b){
	return c.y < b.y; 
}

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