#include<bits/stdc++.h>
using namespace std;
int n,ans=0;
double d,x[1010],y[1010],du;
struct duck{
	double l,r;
}a[1010];
double cmp(duck aa,duck bb){
	return aa.r<bb.r;
}
int main(){
    freopen("monitor.in","r",stdin);
    freopen("monitor.out","w",stdout);
	cin>>n>>d;
	for(int i=1;i<=n;i++){
		cin>>x[i]>>y[i];
		if(y[i]>d){
			cout<<"-1"<<endl;
			return 0;
		}
		a[i].l=x[i]-sqrt(d*d-y[i]*y[i]);
		a[i].r=x[i]+sqrt(d*d-y[i]*y[i]);
	}
	sort(a+1,a+n+1,cmp);
	for(int i=1;i<=n;i++){
		if(i==1) du=a[i].r,ans++;
		else if(du>a[i].l) continue;
		else du=a[i].r,ans++;
	}
	cout<<ans<<endl;
	return 0;
}