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 inv_gcd(a, b):
        a = a % b
        if a == 0:
            return (b, 0)
        s = b;
        t = a
        m0 = 0;
        m1 = 1
        while (t):
            u = s // t
            s -= t * u
            m0 -= m1 * u
            s, t = t, s
            m0, m1 = m1, m0
        if m0 < 0:
            m0 += b // s
        return (s, m0)
    def crt(r, m):
        assert len(r) == len(m)
        n = len(r)
        r0 = 0;
        m0 = 1
        for i in range(n):
            assert 1 <= m[i]
            r1 = r[i] % m[i]
            m1 = m[i]
            if m0 < m1:
                r0, r1 = r1, r0
                m0, m1 = m1, m0
            if (m0 % m1 == 0):
                if (r0 % m1 != r1):
                    return (0, 0)
                continue
            g, im = inv_gcd(m0, m1)
            u1 = m1 // g
            if ((r1 - r0) % g):
                return (0, 0)
            x = (r1 - r0) // g % u1 * im % u1
            r0 += x * m0
            m0 *= u1
            if r0 < 0:
                r0 += m0
        return (r0, m0)
    N,M = MI()
    A = LI()
    B = LI()
    Same = []
    for a in range(N):
        for b in range(M):
            if(A[a] == B[b]):
                Same.append((a,b))
                if(a==b):
                    print(a+1)
                    exit()
    if not (Same):
        print(-1)
        exit()
    C = [N,M]
    Ans = INF
    for a,b in Same:
        R = [a,b]
        r, m = crt(R, C)
        #print(r,m)
        if(r==0 and m==0):
            continue
        Ans = min(Ans,r+1)
    if(Ans == INF):
        print(-1)
        exit()
    print(Ans)
    return
solve()