import sys

input = sys.stdin.buffer.readline
h, w, n = map(int, input().split())
num = 10 ** 5
graph = [[] for _ in range(2 * num)]
start = set()
edges = {}
e = {}
for i in range(n):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    b += num
    graph[a].append(b)
    graph[b].append(a)
    start.add(a)
    edges[(a, b)] = i
    edges[(b, a)] = i
    e[i] = (a, b)


used = [0] * num * 2


# graph and n is necessary
def dfs(start):
    par = [-1] * num * 2
    depth = [-1] * num * 2
    size = [0] * num * 2
    stack = []
    stack.append(~start)
    stack.append(start)
    euler = []
    while stack:
        v = stack.pop()
        if v >= 0:
            d = depth[v]
            used[v] = 1
            euler.append(v)
            for u in graph[v]:
                if par[v] == u:
                    continue
                if used[u]:
                    euler.append(u)
                    return 1, euler
                par[u] = v
                stack.append(~u)
                stack.append(u)
        else:
            a = ~v
            if euler:
                euler.pop()

    return 0, []


for s in start:
    if used[s]:
        continue
    flag, euler = dfs(s)
    if flag:
        ans = []
        for u, v in zip(euler, euler[1:]):
            ans.append(edges[(u, v)] + 1)
        if len(ans) % 2:
            continue
        if len(ans) >= 4:
            a, b = ans[0], ans[1]
            x1, y1 = e[a - 1]
            x2, y2 = e[b - 1]
            if y1 == y2:
                ans = ans[::-1]
            print(len(ans))
            print(*ans)
            exit()


print(-1)