CSES - Message Route
  • Time limit: 1.00 s
  • Memory limit: 512 MB
Syrjälä's network has $n$ computers and $m$ connections. Your task is to find out if Uolevi can send a message to Maija, and if it is possible, what is the minimum number of computers on such a route.


The first input line has two integers $n$ and $m$: the number of computers and connections. The computers are numbered $1,2,\dots,n$. Uolevi's computer is $1$ and Maija's computer is $n$.

Then, there are $m$ lines describing the connections. Each line has two integers $a$ and $b$: there is a connection between those computers.

Every connection is between two different computers, and there is at most one connection between any two computers.


If it is possible to send a message, first print $k$: the minimum number of computers on a valid route. After this, print an example of such a route. You can print any valid solution.

If there are no routes, print "IMPOSSIBLE".

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

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

1 4 5