from collections import deque


def dfs(H, W, G):
    que = deque()
    parents = [None] * (H + W)
    nonvisited = set(range(H + W))
    while nonvisited:
        x = next(iter(nonvisited))  # get single element from set but not remove
        que.append((x, -1, -1))
        while que:
            x, p, j = que.pop()
            parents[x] = (p, j)
            nonvisited.remove(x)

            for y, i in G[x]:
                if parents[x] == (y, i):
                    continue
                if y in nonvisited:
                    que.append((y, x, i))
                else:
                    return x, y, i, parents
    print(-1)
    exit()


H, W, N = map(int, input().split())
G = [[] for _ in range(H + W)]
points = [None] * N
for i in range(1, N + 1):
    x, y = map(lambda x: int(x) - 1, input().split())
    y += H
    G[x].append((y, i))
    G[y].append((x, i))
    points[i - 1] = (x, y)

X, Y, I, parents = dfs(H, W, G)
path = [I]
while X != Y:
    path.append(parents[X][1])
    X, _ = parents[X]

if points[path[0] - 1][1] != points[path[1] - 1][1]:
    assert points[path[0] - 1][0] == points[path[1] - 1][0]
    path = path[::-1]  # pathは偶数長なので単に反転させるだけでよい
print(len(path))
print(*path)