#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
#define  x first
#define y second 
typedef pair<double,double> PII;
PII a[1010];
PII b[1010];
int x,y;
bool cmp(PII a,PII b){
    return a.second<b.second;
}
int main(){
    int n,d;
    cin>>n>>d;
    for(int i=0;i<n;i++){
        cin>>x>>y;
        if(y>d){
            puts("-1");
            return 0;
        }
        double len=sqrt(d*d-y*y);
        a[i].first=x-len;
        a[i].second=x+len;
    }
    sort(a,a+n,cmp);
    int ans=1;
    double x0=a[0].second;
    for(int i=1;i<n;i++){
        if(x0>=a[i].first)continue;
        else{
            ans++;
            x0=a[i].second;
        }
    }
    cout<<ans;

}