import sys
input = sys.stdin.readline

H, W, N = map(int, input().split())
G = [set() for _ in range(H+W)]
for i in range(N):
    x, y = map(lambda x: int(x) - 1, input().split())
    G[x].add((H+y, i))
    G[H+y].add((x, i))
st = []
for v in range(H+W):
    if len(G[v]) == 1:
        st.append(v)
while st:
    v = st.pop()
    for u, i in G[v]:
        G[u].remove((v, i))
        if len(G[u]) == 1:
            st.append(u)
    G[v] = set()
prev = [None] * (H+W)
for s in range(H):
    if prev[s] is not None:
        continue
    st = [(s, -1, -1)]
    while st:
        v, p, j = st.pop()
        prev[v] = (p, j)
        for u, i in G[v]:
            if (u, i) == prev[v]:
                continue
            if u == s:
                ans = [i]
                while v != s:
                    v, i = prev[v]
                    ans.append(i)
                print(len(ans))
                print(*map(lambda x: x + 1, ans[::-1]))
                exit()
            if prev[u] is None:
                st.append((u, v, i))
print(-1)