mod = 1000000007
eps = 10**-9
NN = 2*10 ** 5


def main():
    import sys
    from collections import deque
    input = sys.stdin.buffer.readline

    H, W, N = map(int, input().split())
    adj = [[] for _ in range(H + W + 1)]
    E_idx = {}
    for i in range(1, N+1):
        x, y = map(int, input().split())
        E_idx[x * (NN+1) + y + H] = i
        E_idx[(y + H) * (NN+1) + x] = i
        adj[x].append(y + H)
        adj[y + H].append(x)

    seen = [-1] * (H + W + 1)
    par = [0] * (H + W + 1)
    for v0 in range(1, H+1):
        if seen[v0] != -1:
            continue
        que = deque()
        que.append(v0)
        seen[v0] = 0
        B = []
        while que:
            v = que.popleft()
            for u in adj[v]:
                if seen[u] == -1:
                    seen[u] = seen[v] + 1
                    par[u] = v
                    que.append(u)
                else:
                    if u != par[v]:
                        B.append((u, v))
        if B:
            u, v = B[0]
            U = []
            uu = u
            while uu != v0:
                U.append(uu)
                uu = par[uu]
            V = []
            vv = v
            while vv != 0:
                V.append(vv)
                vv = par[vv]
            V.reverse()
            U.extend(V)
            if U[0] > H:
                U_new = [U[-1]] + U[:-1]
                U = U_new
            ans = []
            L = len(U)
            for i in range(L):
                x, y = U[i], U[(i+1)%L]
                if x > y:
                    x, y = y, x
                #print(x, y)
                ans.append(E_idx[x * (NN+1) + y])
            assert len(ans) % 2 == 0
            print(len(ans))
            print(*ans)
            exit()
    #print(seen)
    print(-1)


if __name__ == '__main__':
    main()