import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = 10**16
md = 998244353
# md = 10**9+7

h,w,n=LI()
to=[[] for _ in range(h+w)]

for _ in range(n):
    x,y=LI1()
    y+=h
    to[x].append(y)
    to[y].append(x)

vis=[0]*(h+w)
def dfs(u,par=-1):
    vis[u]=1
    for v in to[u]:
        if v==par:continue
        if vis[v]==2:continue
        if vis[v]==1:return [v,u]
        ret=dfs(v)
        if ret:
            if ret[0]==ret[-1]:return ret
            return ret+[u]
    vis[u]=2
    return []

ans=[]
for u in range(h):
    uu=dfs(u)
    if uu:
        ans=[u+1 for u in uu[1:]]
        break

if ans:
    print(len(ans))
    print(*ans)
else:
    print(-1)