import sys
input = sys.stdin.readline # for fast input...
 
# graph input. n->no of nodes, m->no of edges...
n,m = map(int, input().split())

# constructing bidirectional graph...
# I am using '0' based graph indexing...
graph = [[] for _ in range(n)]
for _ in range(m):
	a,b = map(int, input().split())
	graph[a-1].append(b-1)
	graph[b-1].append(a-1)
 
g = 0 # g is an indicator variable, g->1 means "impossible". 

# degree of each node should be even for Eulerian cycle in undirected graph...
for i in graph:
	if len(i)%2:
		g = 1
		break
if g:
	print("IMPOSSIBLE")
else:
# using stacked method to find Eulerian path to avoid recursion (method link given)...
	stack = [0]
	path = []
	while stack:
		node = stack[-1]
		if len(graph[node]) == 0:
			path.append(node+1)
			stack.pop()
		else:
			nextNode = graph[node][-1]
			graph[nextNode].remove(node)  # I think this is the bottleneck because remove operation is not O(1).
			graph[node].remove(nextNode)
			stack.append(nextNode)
	if len(path) == m+1:
		print(*path)
	else:
		print("IMPOSSIBLE")