#include<iostream>
#include<cmath>
#include<algorithm>
using namespace std;
typedef pair<double,double> PII;
const int N = 1010;
PII q[N];
int n,d;

int main(){
    scanf("%d%d",&n,&d);
    
    bool is_failed = false;
    for(int i=0;i<n;i++){
        int x,y;
        scanf("%d%d",&x,&y);
        if(y>d) is_failed = true;
        else {
            double len = sqrt(d*d - y*y);
            q[i] = {x+len,x-len};
        }
    }
    
    if(is_failed){
        puts("-1");
    }else {
        sort(q,q+n);
        int cnt = 0;
        double last = -1e9;
        for(int i=0;i<n;i++){
            if(last<q[i].second){
                cnt++;
                last = q[i].first;
            }
        }
        printf("%d",cnt);
    }
    
}