import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)

H, W, N = map(int, input().split())
X = [-1] * N
Y = [-1] * N
row = [[] for _ in range(H+1)]
col = [[] for _ in range(W+1)]
for i in range(N):
    X[i], Y[i] = map(int, input().split())
    row[X[i]].append(i)
    col[Y[i]].append(i)

v0 = [0] * N
v1 = [0] * N

pos = [X, Y]
G = [row, col]
vis = [v0, v1]
tour = []


def dfs(s, F, p=-1):
    vis[F][s] = 1
    tour.append(s + 1)
    for t in G[F][pos[F][s]]:
        if t == p or t == s:
            continue
        if vis[1-F][t]:
            tour.append(t + 1)
            return True
        if dfs(t, 1-F, s):
            return True
    tour.pop()
    return False


for i in range(N):
    if vis[0][i]:
        continue
    tour = []
    if dfs(i, 0):
        tour.reverse()
        last = tour.pop()
        idx = tour.index(last)
        print(len(tour) - idx)
        print(*tour[idx:])
        exit()
print(-1)