#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<cmath>
using namespace std;
const int N = 1010;
int n, d;
pair<double, double> seg[N];
int main()
{
    cin >> n >> d;
    bool failed = false;
    for (int i = 0; i < n; i++) {
        int x, y;
        cin >> x >> y;
        if (y > d)
            failed = true;
        if (failed == true)
            break;
        else {
            double len = sqrt(d * d - y * y);

            seg[i] = make_pair(x +len, x - len);
        }
    }
    if (failed) {
        puts("-1");
    }
    else {
        sort(seg, seg + n);
        int cnt = 0;
        double last = -1e20;
        for (int i = 0; i < n; i++) {
            if (last < seg[i].second) {
              //  cout<<seg[i].first<<' '<<seg[i].second<<endl;
                cnt++;
                last = seg[i].first;
            }

        }
        cout << cnt << endl;

    }

    return 0;
}