import sys
sys.setrecursionlimit(1000000)


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

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

for idx in range(n):
    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)


def output(t, is_h):
    t.reverse()
    if not is_h:
        t = t[1:] + t[:1]

    print(len(t))
    print(*(i+1 for i in t))


def dfs(i, prev=-1):
    if visited[i]:
        return [], i
    is_h = i < h
    visited[i] = True

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

        t, start = dfs(j, i)
        if start != -1:
            t.append(idx)

            if start == i:
                output(t, is_h)
                exit()

            return t, start

    return [], -1


for i in range(h + w):
    if not visited[i]:
        dfs(i)
print(-1)