在一個N x N的平面上 (1 <= N <= 500)，有K塊隕石 (1 <= K <= 10,000)，分別在一些格子中。卡恩想要用他的強者光束把所有隕石給清除，每一次使用強者光束都可以把某一整行或一整列的隕石給消滅。但由於卡恩對演算法的狂熱，他除了要清除所有隕石，還希望使用最少次的強者光束。
今給出所有隕石的位置，試問最少要使用幾次強者光束，才能把所有的隕石消滅？

(原文)
Bessie wants to navigate her spaceship through a dangerous asteroid field in the shape of an N x N grid (1 <= N <= 500). The grid contains K asteroids (1 <= K <= 10,000), which are conveniently located at the lattice points of the grid.
Fortunately, Bessie has a powerful weapon that can vaporize all the asteroids in any given row or column of the grid with a single shot. This weapon is quite expensive, so she wishes to use it sparingly.
Given the location of all the asteroids in the field, find the minimum number of shots Bessie needs to fire to eliminate all of the asteroids.