二维平面内有N(N≤10^6)个点，有一个激光发射器和一个接收器。现在要在点上安装镜子（光线只能垂直于坐标轴），问最少安装几个镜子才能让接收器收到激光 ，或不可能。
输入描述:
The first line of input contains 5 space-separated integers: N,xL,yL,xB,yB, where (xL,yL) is the location of the laser and (xB,yB) is the location of the barn. All coordinates are between 0 and 1,000,000,000.
The next N lines each contain the x and y locations of a fence post, both integers in the range 0…1,000,000,000.
输出描述:
Please output the minimum number of mirrors needed to direct the laser to the barn, or -1 if this is impossible to do.
示例1
输入
复制
4 0 0 7 2
3 2
0 2
1 6
3 0