import sys
sys.setrecursionlimit(1000000)


h, w, n = map(int, input().split())

edge = [[] for _ in range(h + w)]

for idx in range(1, n+1):
    x, y = [int(i) - 1 for i in input().split()]
    y = y + h
    edge[x].append((y, idx))
    edge[y].append((x, idx))

visited = [False] * (h + w)
parent = [None] * (h + w)


def output(start):
    t = []
    i = start
    while True:
        i, site = parent[i]
        t.append(site)

        if i == start:
            break

    if i >= h:
        t = t[1:] + t[:1]

    print(len(t))
    print(*t)


def dfs(start):
    stack = [(-1, start)]

    while stack:
        prev, i = stack[-1]
        stack.pop()

        if visited[i]:
            return i

        visited[i] = True

        for j, idx in edge[i]:
            if j == prev:
                continue

            stack.append((i, j))
            parent[j] = (i, idx)

    return -1


for i in range(h + w):
    if not visited[i]:
        result = dfs(i)

        if result != -1:
            output(result)
            exit()
print(-1)