Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(1000000000)
from collections import defaultdict

ans=[]
V=defaultdict(list)

N,M=map(int,input().split())

a,b=map(int,input().split())
V[a].append(b)
V[b].append(a)
ans.append(a)
ans.append(b)

for i in range(1,M):
  a,b=map(int,input().split())
  V[a].append(b)
  V[b].append(a)

def solve(li):
  s=li[0]
  e=li[-1]
  for v in V[s]:
    if not(v in li):
      return solve([v]+li)
  for v in V[e]:
    if not(v in li):
      return solve(li+[v])
  print(len(li))
  print(*li)
  return

solve(ans)


Fixed submission:
import sys
sys.setrecursionlimit(1000000000)

from collections import defaultdict
N, M = [int(_) for _ in input().split()]
V = defaultdict(list)
for i in range(M):
    A, B = [int(_) for _ in input().split()]
    V[A].append(B)
    V[B].append(A)

def solve(N, M, V):
    result = [1, V[1][0]]
    used = [False] * (N + 1)
    for x in result:
        used[x] = True

    def check_edge(i):
        for e in V[result[i]]:
            if not used[e]:
                if i == -1:
                    result.append(e)
                else:
                    result.insert(i, e)
                used[e] = True
                return True
        return False

    while True:
        if check_edge(0): continue
        if check_edge(-1): continue
        return result

result = solve(N, M, V)
print(len(result))
print(*result)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(1000000000)
from collections import defaultdict

ans=[]
V=defaultdict(list)

N,M=map(int,input().split())

a,b=map(int,input().split())
V[a].append(b)
V[b].append(a)
ans.append(a)
ans.append(b)

for i in range(1,M):
  a,b=map(int,input().split())
  V[a].append(b)
  V[b].append(a)

def solve(li):
  s=li[0]
  e=li[-1]
  for v in V[s]:
    if not(v in li):
      return solve([v]+li)
  for v in V[e]:
    if not(v in li):
      return solve(li+[v])
  print(len(li))
  print(*li)
  return

solve(ans)


Fixed submission:
import sys
sys.setrecursionlimit(1000000000)

from collections import defaultdict
N, M = [int(_) for _ in input().split()]
V = defaultdict(list)
for i in range(M):
    A, B = [int(_) for _ in input().split()]
    V[A].append(B)
    V[B].append(A)

def solve(N, M, V):
    result = [1, V[1][0]]
    used = [False] * (N + 1)
    for x in result:
        used[x] = True

    def check_edge(i):
        for e in V[result[i]]:
            if not used[e]:
                if i == -1:
                    result.append(e)
                else:
                    result.insert(i, e)
                used[e] = True
                return True
        return False

    while True:
        if check_edge(0): continue
        if check_edge(-1): continue
        return result

result = solve(N, M, V)
print(len(result))
print(*result)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(1000000000)
from collections import defaultdict

ans=[]
V=defaultdict(set)

N,M=map(int,input().split())

a,b=map(int,input().split())
V[a].add(b)
V[b].add(a)
ans.append(a)
ans.append(b)

for i in range(1,M):
  a,b=map(int,input().split())
  V[a].add(b)
  V[b].add(a)

def solve(li):
  s=li[0]
  e=li[-1]
  for v in V[s]:
    if not(v in li):
      return solve([v]+li)
  for v in V[e]:
    if not(v in li):
      return solve(li+[v])
  print(len(li))
  print(*li)
  return

solve(ans)


Fixed submission:
import sys
sys.setrecursionlimit(1000000000)

from collections import defaultdict
N, M = [int(_) for _ in input().split()]
V = defaultdict(list)
for i in range(M):
    A, B = [int(_) for _ in input().split()]
    V[A].append(B)
    V[B].append(A)

def solve(N, M, V):
    result = [1, V[1][0]]
    used = [False] * (N + 1)
    for x in result:
        used[x] = True

    def check_edge(i):
        for e in V[result[i]]:
            if not used[e]:
                if i == -1:
                    result.append(e)
                else:
                    result.insert(i, e)
                used[e] = True
                return True
        return False

    while True:
        if check_edge(0): continue
        if check_edge(-1): continue
        return result

result = solve(N, M, V)
print(len(result))
print(*result)

Buggy python submission (verdict: Runtime Error):
from collections import defaultdict

ans=[]
V=defaultdict(set)

N,M=map(int,input().split())

a,b=map(int,input().split())
V[a].add(b)
V[b].add(a)
ans.append(a)
ans.append(b)

for i in range(1,M):
  a,b=map(int,input().split())
  V[a].add(b)
  V[b].add(a)

def solve(li):
  s=li[0]
  e=li[-1]
  for v in V[s]:
    if not(v in li):
      return solve([v]+li)
  for v in V[e]:
    if not(v in li):
      return solve(li+[v])
  print(len(li))
  print(*li)
  return

solve(ans)

Fixed submission:
import sys
sys.setrecursionlimit(1000000000)

from collections import defaultdict
N, M = [int(_) for _ in input().split()]
V = defaultdict(list)
for i in range(M):
    A, B = [int(_) for _ in input().split()]
    V[A].append(B)
    V[B].append(A)

def solve(N, M, V):
    result = [1, V[1][0]]
    used = [False] * (N + 1)
    for x in result:
        used[x] = True

    def check_edge(i):
        for e in V[result[i]]:
            if not used[e]:
                if i == -1:
                    result.append(e)
                else:
                    result.insert(i, e)
                used[e] = True
                return True
        return False

    while True:
        if check_edge(0): continue
        if check_edge(-1): continue
        return result

result = solve(N, M, V)
print(len(result))
print(*result)