11 人解决，20 人已尝试。
19 份提交通过，共有 74 份提交。
6.5 EMB 奖励。
单点时限: 2.0 sec
内存限制: 256 MB
The Public Peace Commission should be legislated in Parliament of The Democratic Republic of Byteland according to The Very Important Law. Unfortunately one of the obstacles is the fact that some deputies do not get on with some others.
The Commission has to fulfill the following conditions:
Each party has exactly two deputies in the Parliament. All of them are numbered from $1$ to $2n$. Deputies with numbers $2i-1$ and $2i$ belong to the $i$-th party .
Write a program, which:
In the first line there are two non-negative integers $n$ and $m$. They denote respectively: the number of parties, $1 \le n \le 8000$, and the number of pairs of deputies, who do not like each other, $0 \le m \le 20000$. In each of the following $m$ lines there is written one pair of integers $a$ and $b$, $1 \le a < b \le 2n$, separated by a single space. It means that the deputies $a$ and $b$ do not like each other.
Output should contain one word
NO in Polish), if the setting up of the Commission is impossible. In case when setting up of the Commission is possible the output should contain $n$ integers from the interval from $1$ to $2n$, written in the ascending order, indicating numbers of deputies who can form the Commission. Each of these numbers should be written in a separate line. If the Commission can be formed in various ways, your program may write mininum number sequence.
3 2 1 3 2 4
1 4 5