给定如图所示的若干个长条。你可以在某一行的任意两个数之间作一条竖线，从而把这个长条切开，并可能切开其他长条。问至少要切几刀才能把每一根长条都切开。样例如图需要切两刀。

注意：输入文件每行的第一个数表示开始的位置，而第二个数表示长度。

输入描述:

Line 1: A single integer, N(2 <= N <= 32000)
Lines 2..N+1: Each line contains two space-separated positive integers that describe a leash. The first is the location of the leash's stake; the second is the length of the leash.(1 <= length <= 1e7)

输出描述:

Line 1: A single integer that is the minimum number of cuts so that each leash is cut at least once.

7
2 4
4 7
3 3
5 3
9 4
1 5
7 3

2