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



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