VIII Olimpiada Informatyczna 2000/2001

Task: SPO

Author: Wojciech Rytter

II stage contest, the first day 
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 2i1 and 2i belong to the ith party .
Write a program, which:
In the first line of the text file SPO.IN there are two nonnegative integers n and m. They denote respectively: the number of parties, 1<=n<=8000, and the number of pairs of deputies, who do not like each other, 0<=m<=20000. In each of the following m lines there is written one pair of integers a and b, 1<=a<b<=2n, separated by a single space. It means that the deputies a and b do not like each other.
The text file SPO.OUT should contain one word NIE (means NO in Polish), if the setting up of the Commission is impossible. In case when setting up of the Commission is possible the file SPO.OUT 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 any of them.
For the input file SPO.IN:
3 2 1 3 2 4
a correct answer is the output file SPO.OUT.
1 4 5