Description

Input

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.

Output

输出仅一行, 表示最少推倒骨牌的数目

Samples

6
1 1
2 2
3 1
5 1
6 1
8 3

2


Explanation
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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.