CSES - Teleporters Path
  • Time limit: 1.00 s
  • Memory limit: 512 MB
A game has $n$ levels and $m$ teleportes between them. You win the game if you move from level $1$ to level $n$ using every teleporter exactly once.

Can you win the game, and what is a possible way to do it?


The first input line has two integers $n$ and $m$: the number of levels and teleporters. The levels are numbered $1,2,\dots,n$.

Then, there are $m$ lines describing the teleporters. Each line has two integers $a$ and $b$: there is a teleporter from level $a$ to level $b$.

You can assume that each pair $(a,b)$ in the input is distinct.


Print $m+1$ integers: the sequence in which you visit the levels during the game. You can print any valid solution.

If there are no solutions, print "IMPOSSIBLE".

  • $2 \le n \le 10^5$
  • $1 \le m \le 2 \cdot 10^5$
  • $1 \le a,b \le n$

5 6
1 2
1 3
2 4
2 5
3 1
4 2

1 3 1 2 4 2 5