#include<bits/stdc++.h>
int n,m,k,s,t,d;
struct node
{
    double l,r;
}a[100001];
bool cmp(node x,node y)
{
    return x.r<y.r;
}
int main()
{
    std::cin>>n>>d;
    int bo=0;
    for(int i=1;i<=n;i+=1)
    {
        std::cin>>s>>t;
        if(t>d)bo=1;
        else
        {
            double p=sqrt(d*d-t*t);
            a[i]={s-p,s+p};
        }
    }
    std::sort(a+1,a+n+1,cmp);
    int ans=0;
    double now=-2000000000;
    for(int i=1;i<=n;i+=1)if(a[i].l>now)
    {
        ans+=1;
        now=a[i].r;
    }
    if(bo)ans=-1;
    std::cout<<ans<<"\n";
}