#include <bits/stdc++.h>
    using namespace std;
    struct node{
        double x,y;
    }a[1008];
    bool cmp(node a,node b){
        return a.y<b.y;
    }
    int n,r,ans=1;
    bool bj=0;
    int main(){
//        freopen("monitor.in","r",stdin);
//        freopen("monitor.out","w",stdout);     
        cin>>n>>r;
        double x,y;
        for(int i=1;i<=n;i++){
            cin>>x>>y;
            if(y>r){
                bj=1;
            }
            a[i].x=1.0*x-sqrt(1.0*r*r-a[i].y*a[i].y);
            a[i].y=1.0*x+sqrt(1.0*r*r-a[i].y*a[i].y);
        }
        if(bj==1){
            cout<<-1;
            return 0;
        }
        sort(a+1,a+n+1,cmp);
        double pos=a[1].y;
        for(int i=2;i<=n;i++){
            if(a[i].x>pos){
                pos=a[i].y;
                ans++;
            }
            else{
                pos=min(pos,a[i].y);
            }
        }
        cout<<ans;
        
        
        return 0;
    }