- Time limit: 1.00 s
- Memory limit: 512 MB
The first input line has two integers $n$ and $m$: the number of cities and flights. The cities are numbered $1,2,\dots,n$.
Then, there are $m$ lines describing the flights. Each line has two integers $a$ and $b$: there is a flight connection from city $a$ to city $b$. All connections are one-way flights from a city to another city.
First print an integer $k$: the number of cities on the route. Then print $k$ cities in the order they will be visited. You can print any valid solution.
If there are no solutions, print "IMPOSSIBLE".
- $1 \le n \le 10^5$
- $1 \le m \le 2 \cdot 10^5$
- $1 \le a,b \le n$
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