from collections import deque

H, W, N = map(int, input().split())
rows = [[] for _ in range(H)]
columns = [[] for _ in range(W)]

points = []
for i in range(N):
    x, y = (int(x) - 1 for x in input().split())
    points.append((x, y))
    rows[x].append(i)
    columns[y].append(i)

parent = [None] * N
nonvisited = set(range(N))

while nonvisited:
    v0 = nonvisited.pop()
    d = deque([(v0, -1)])
    while d:
        v, p = d.pop()
        parent[v] = p
        nonvisited.discard(v)
        row, col = points[v]
        for x in rows[row] + columns[col]:
            if x == v or x == p:
                continue
            if x in nonvisited:
                d.append((x, v))
            else:
                # cycle found
                ans = [v + 1]
                y = parent[v]
                while y != v and y != -1:
                    ans.append(y + 1)
                    y = parent[y]
                print(len(ans))
                print(*ans)
                exit()
print(-1)