Description

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

Input

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

Output

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.

Sample Input

Sample Output

題意

海上有n多島，在海岸線上（x軸）建一個雷達能覆蓋到與它距離不超過d的島，求覆蓋所有島的最小雷達數。

思路

以島嶼為圓心，d為半徑畫圓，交x軸于s,e兩點，然后以線段末尾為排序標準對所有這樣的線段排序，從左至右依次判斷，假設雷達放置在一個線段的末端，然后忽略它所能涉及到的島嶼。

AC 代碼