#include<cstdio>
#include<algorithm>
#include<set>
using namespace std;
struct info{
	int H,S;
}apple[5010];

bool cmp1(info a,info b)
{
	return a.H<b.H;
}
bool cmp2(info a,info b)
{
	return a.S<b.S;
}

int main()
{
	int n,i,s,a,b;
	scanf("%d%d%d%d",&n,&s,&a,&b);
	for(i=0;i<n;i++)
	{
		scanf("%d%d",&apple[i].H,&apple[i].S);
	}
	sort(apple,apple+n,cmp1);
	for(i=0;apple[i].H<=(a+b);i++);
	sort(apple,apple+i,cmp2);
	i=0;
	while(s>=0&&i<n)
	{
		s-=apple[i].S;
		i++;
	}
	printf("%d",i-1);
	return 0;
}