#include #include #include

using namespace std;

typedef pair<double, double> PDD; const int N = 1010; const double eps = 1e-6, INF = 1e10; // double一般定义一个eps精确值

int n, R; PDD segs[N];

int main() { bool success = true;

cin >> n >> R;
for(int i = 0; i < n; i++)
{
    int x, y;
    cin >> x >> y;
    if(y > R)
    {
        success = false;
        break;
    }
    double len = sqrt(R * R - y * y);
    segs[i] = {x + len, x - len}; //区间 按终点起点排序
}
if(!success) puts("-1");
else
{
    sort(segs, segs + n);
    int res = 0;
    double last = -INF; //***这里要定义double
    for(int i = 0; i < n; i++)
    {
        auto seg = segs[i];
        if(seg.second > last + eps) //seg.second 是起点
        {
            res ++;
            last = seg.first; // seg.first的终点
            
        }
    }
    cout << res << endl;
}
return 0;

}