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