import sys
INF = float('inf')
MOD = 10**9 + 7
MOD2 = 998244353
def solve():
    def II(): return int(sys.stdin.readline())
    def LI(): return list(map(int, sys.stdin.readline().split()))
    def LC(): return list(input())
    def IC(): return [int(c) for c in input()]
    def MI(): return map(int, sys.stdin.readline().split())

    def egcd(a, b):
        if a == 0:
            return b, 0, 1
        else:
            g, y, x = egcd(b % a, a)
            return g, x - (b // a) * y, y

    def chineseRem(b1, m1, b2, m2):
        # 中国剰余定理
        # x ≡ b1 (mod m1) ∧ x ≡ b2 (mod m2) <=> x ≡ r (mod m)
        # となる(r. m)を返す
        # 解無しのとき(0, -1)
        d, p, q = egcd(m1, m2)
        if (b2 - b1) % d != 0:
            return 0, -1
        m = m1 * (m2 // d)  # m = lcm(m1, m2)
        tmp = (b2 - b1) // d * p % (m2 // d)
        r = (b1 + m1 * tmp) % m
        return r, m
    N,M = MI()
    A = LI()
    B = LI()
    Ans = INF
    for a in range(N):
        for b in range(M):
            if(A[a] == B[b]):
                R = [a, b]
                r, m = chineseRem(a,N,b,M)
                if (r == 0 and m == -1):
                    continue
                if (Ans > r + 1):
                    Ans = r + 1
    if(Ans == INF):
        print(-1)
        exit()
    print(Ans)
    return
solve()