Longest Flight Route#11450
Uolevi has won a contest, and the prize is a free flight trip that can consist of one or more flights through cities. Naturally, Uolevi wants to choose a trip visiting as many cities as possible.
Uolevi wishes to travel from Syrjälä to Lehmälä, visiting the maximum number of cities. You are given a list of possible flights, and you know that there are no directed cycles in the flight network.
The first line contains two integers (2 \le n \le 10^5) and (1 \le m \le 2 \cdot 10^5) — the number of cities and the number of flights. The cities are numbered 1, 2, \ldots, n. City is Syrjälä, and city is Lehmälä.
Next, there are lines describing the flights. Each line contains two integers and (1 \le a, b \le n) — there is a flight from city to city . All flights are one-way only.
First, print the maximum number of cities on the route. Then, print the cities in the order they will be visited. You may print any valid solution.
If there is no solution, print "IMPOSSIBLE".
Example 1