输入第一行一个整数N, 代表有N个骨牌. 以下N行每行两个数Pi Hi, 分别表示第I个骨牌的位置和高度.
输出仅一行, 表示最少推倒骨牌的数目
6 1 1 2 2 3 1 5 1 6 1 8 3
2 Explanation | | | | | | | | | 1 2 3 4 5 6 7 8 Pushing 1 causes 2 and 3 to fall, while pushing 8 causes 6 to fall and gently makes 5 tip over as well.
