Description

Winter vacation has arrived, and Xiao Tu can finally enjoy watching TV happily. However, there are too many programs that Xiao Tu likes, and he hopes to watch as many complete programs as possible.

Now he gives you the broadcast schedule of his favorite TV programs. Can you help him arrange a reasonable viewing plan?

Input Format

The input contains multiple test cases. The first line of each test case is an integer n (n ≤ 100), representing the total number of programs Xiao Tu likes.

The next n lines each contain two integers, si and ei (1 ≤ i ≤ n), representing the start and end times of the i-th program. To simplify the problem, each time is represented by a positive integer.

When n = 0, the input ends.

Output Format

For each test case, output the number of complete TV programs that can be watched.

```input1 12 1 3 3 4 0 7 3 8 15 19 15 20 10 15 8 18 6 12 5 10 4 14 2 9 0 ``` ```output1 5 ``` ## 译文

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