1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int N = 1010;
 4 const double eps = 1e-6, INF = 1e10;
 5 //eps用于精度判断
 6 typedef pair<double, double> pdd;
 7 pdd segs[N];
 8 int main() {
 9     int n, r;
10     cin >> n >> r;
11     for (int i = 0; i < n; i++) {
12         int x, y;
13         cin >> x >> y;
14         if (y > r) {
15             cout << -1 << endl;
16             return 0;
17         }
18         double len = sqrt(r * r - y * y);
19         segs[i] = {x + len, x - len};
20         //需要按照右端点从小到大排序
21         //所以first和second交换一下
22         //second是起点，first是终点
23     }
24     sort(segs, segs + n);
25     int res = 0;
26     double last = -INF;
27     //last是上一个雷达的位置，初始化为负无穷
28     for (int i = 0; i < n; i++) { //扫描一遍
29         if (segs[i].second > last + eps) { //如果当前起点，大于上一个终点
30             res++;
31             last = segs[i].first;
32         }
33     }
34     cout << res << endl;
35     return 0;
36 }