Assume the coasting is an infinite straight line. Land is in one side of coasting, sea in the other. Each small island is a point locating in the sea side. And any radar installation, locating on the coasting, can only cover d distance, so an island in the sea can be covered by a radius installation, if the distance between them is at most d.

We use Cartesian coordinate system, defining the coasting is the x-axis. The sea side is above x-axis, and the land side below. Given the position of each island in the sea, and given the distance of the coverage of the radar installation, your task is to write a program to find the minimal number of radar installations to cover all the islands. Note that the position of an island is represented by its x-y coordinates.



Figure A Sample Input of Radar Installations

The input consists of several test cases. The first line of each case contains two integers n (1<=n<=1000) and d, where n is the number of islands in the sea and d is the distance of coverage of the radar installation. This is followed by n lines each containing two integers representing the coordinate of the position of each island. Then a blank line follows to separate the cases.

The input is terminated by a line containing pair of zeros

For each test case output one line consisting of the test case number followed by the minimal number of radar installations needed. "-1" installation means no solution for that case.

3 2

1 2

-3 1

2 1

1 2

0 2

0 0

Case 1: 2

Case 2: 1

题目大意：
就是给你n组数据和圆的半径d，让你在x轴上画半径为d的圆，问：如果将所有的点都画进去，最少需要多少个圆，这个题目和导弹拦截有点像，不过更加简单

思路：
就是先判断d是不是大于等于0，如果d<0，肯定是输出-1的，
之后输入数字，如果有坐标的纵坐标比d还要大，那么也是不对的也要输出-1
之后对坐标进行处理，把每一个坐标在x轴上的范围标记出来，并进行排序，先排右边的位置，右边位置越小就排在越前面，因为我们是要从横坐标左边往右边排
如果右边相同，就排左边，左边大的先排，因为区间范围小的肯定可以把区间范围大的包括进去，反之则不行。
排完序之后
就开始画圈圈。

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <algorithm>

#include <math.h>

#include <iostream>

using namespace std;

const int maxn=1010;

struct node

{

    double l,r;

}exa[maxn];

bool cmp(node a,node b)

{

    if(a.r==b.r) return a.l>b.l;

    return a.r<b.r;

}

int main()

{

    int n,cnt=0;;

    double d,a,b;

    while(scanf("%d%lf",&n,&d)!=EOF&&(n+d))

    {

        bool flag=0;

        if(d>=0) flag=1;

        for(int i=0;i<n;i++)

        {

            scanf("%lf%lf",&a,&b);

            if(b>d) flag=0;

            if(flag)

            {

                exa[i].l=a-sqrt(d*d-b*b);

                exa[i].r=a+sqrt(d*d-b*b);

            }

        }

        sort(exa,exa+n,cmp);

        int ans=-1;

        if(flag)

        {

            ans=1;

            double maxr=exa[0].r;

            for(int i=1;i<n;i++)

            {

                if(exa[i].l>maxr)

                {

                    ans++;

                    maxr=exa[i].r;

                }

            }

        }

        cout << "Case " << ++cnt << ": " << ans << endl;

    }

    return 0;

}