INF = 10 ** 15

N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

result = INF
for i in range(N):
    a = A[i]
    for j in range(M):
        x = i + j * N
        if x > result:
            break
        b = B[x % M]
        if a != b:
            continue
        result = min(result, x)
        break
if result == INF:
    print(-1)
else:
    print(result)