#include<bits/stdc++.h>
using namespace std;
typedef pair<double,double> PDD;
#define l first
#define r second
const int N=1010;
PDD range[N]; 
bool cmp(PDD a,PDD b)
{
    return a.r<b.r;
}
int main()
{
	int n,d;
	cin>>n>>d;
	for(int i=0;i<n;i++)
	{
		int x,y;
		cin>>x>>y;
		if(y>d)
		{
			cout<<"-1"<<endl;
			return 0;
		}
		double len=sqrt(d*d-y*y);
		range[i]={x-len,x+len}; //得到可以覆盖当前小岛的雷达可安装范围
	}
	sort(range,range+n,cmp); //从小到大排序
	int res=0;
	double ed=-2e9; 
	for(int i=0;i<n;i++)
	{
		if(range[i].l>=ed)
		{
		    res++;
		    ed=range[i].r;
		}
	}
	cout<<res;
	return 0;
}