#include<bits/stdc++.h>
using namespace std;

typedef pair<double, double> PDD;

const int N = 1010;
const double eps = 1e-6, INF = 1e10;

int n, d;
PDD seg[N];

int main()
{
    cin >> n >> d;
    bool success = true;

    for (int i = 0; i < n; i++) 
    {
        int x, y;
        cin >> x >> y;
        if (y > d) // 因为雷达只能建在坐标轴上，如果小岛的y坐标大于雷达范围，就说明不存在解 
        {
            success = false;
            break;
        }
        auto len = sqrt(d * d - y * y);
        seg[i] = {x + len, x - len};
    }
    if(!success) puts("-1"); 
    else
    {
        sort(seg, seg + n); 
        int res = 0;
        double last = -INF;
        for (int i = 0; i < n; i++)
        {
            if (seg[i].second > last + eps)
            {
                res ++;
                last = seg[i].first;
            }
        }

        cout << res << endl;
    }
    return 0;
}