单点时限: 2.0 sec
内存限制: 256 MB
Foxity and Foxitu are good friends. They like to play number games. One day, Foxity played ICPC with his teammates, leaving Foxitu alone at labs. So he played a number game with himself.
There are $n$ numbers from $1$ to $n$ in a set, each time he can choose two distinct number $a$ and $b$($a \ne b$). He firstly remove $ a $ and $ b $ from this set, then insert $a+b$ and $ \lvert a-b \rvert $ to the set. His goal is to leave the set with only two elements, and He can only operate on this set at most $ n $ times.
Please provide any of his possible operation sequence.
There will be no identical elements in the set, and identical elements are treated as one element.
One line contains one integer $ n(2 \le n \le 10^5) $ ,which is the size of the set.
The first line contains an integer $m$, which is the number of operations.
Follow $m$ lines with two integer $a$ and $b$, which represents each operation.
5 4 5 1 9 3 7 2 8 4 6
3 1 6 2 5 3 4
We guarantee that the first $9$ test data satisfying that $n$ is less than $11$.