Longest route

n, m = [int(x) for x in input().split()]
graph = [[] for _ in range(n)]
for _ in range(m):
    a, b = [int(x) for x in input().split()]
    graph[b-1].append(a-1)

order = []
in_process = set([])
processed = set([])
impossible = False

def dfs_rec(x):
    global impossible
    
    in_process.add(x)
    for c in graph[x]:
        if c in in_process:
            impossible = True
            break
        if c not in processed:
            dfs_rec(c)
    order.append(x)
    in_process.remove(x)
    processed.add(x)

for i in range(n):
    if i not in processed:
        dfs_rec(i)

if impossible:
    print('IMPOSSIBLE')
else:
    nbr_nodes = [float('inf')] * n
    nbr_nodes[0] = 1
    nodes = [[] for _ in range(n)]

    for i, node in enumerate(order):
        maxi = 0
        chosen_node = -1
        for parent in graph[node]:
            if nbr_nodes[parent]+1 > maxi:
                maxi = nbr_nodes[parent]+1
                chosen_node = parent 
        if maxi != 0:
            nbr_nodes[node] = maxi
            nodes[node] = nodes[parent].copy()
            nodes[node].append(parent)

    if nbr_nodes[n-1] == float('inf'):
        print('IMPOSSIBLE')
    else:
        print(nbr_nodes[n-1])
        for node in nodes[n-1]:
            print(node+1, end=' ')
        print(n)

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: RUNTIME ERROR

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: RUNTIME ERROR

Test 16

Verdict: ACCEPTED

Test 17

Verdict: RUNTIME ERROR

Test 18

Verdict: ACCEPTED

Test 19

Verdict: WRONG ANSWER

Test 20

Verdict: RUNTIME ERROR

Test 21

Verdict: WRONG ANSWER