from math import gcd


def isprime(n):
    if n <= 1:
        return False
    elif n == 2:
        return True
    elif n % 2 == 0:
        return False

    A = [2, 325, 9375, 28178, 450775, 9780504, 1795265022]
    s = 0
    d = n - 1
    while d % 2 == 0:
        s += 1
        d >>= 1

    for a in A:
        if a % n == 0:
            return True
        x = pow(a, d, n)
        if x != 1:
            for t in range(s):
                if x == n - 1:
                    break
                x = x * x % n
            else:
                return False
    return True


def pollard(n):
    if n % 2 == 0:
        return 2
    if isprime(n):
        return n

    f = lambda x: (x * x + 1) % n

    step = 0
    while 1:
        step += 1
        x = step
        y = f(x)
        while 1:
            p = gcd(y - x + n, n)
            if p == 0 or p == n:
                break
            if p != 1:
                return p
            x = f(x)
            y = f(f(y))


def primefact(n):
    if n == 1:
        return []
    p = pollard(n)
    if p == n:
        return [p]
    left = primefact(p)
    right = primefact(n // p)
    left += right
    return sorted(left)


def primedict(n):
    P = primefact(n)
    ret = {}
    for p in P:
        ret[p] = ret.get(p, 0) + 1
    return ret


def divisor_lst(n):
    if n == 1:
        return [1]
    primes = primefact(n)
    primes.append(primes[-1] + 1)
    bef = primes[0]
    cnt = 0
    ret = [1]
    for p in primes:
        if p == bef:
            cnt += 1
        else:
            times = bef
            le = len(ret)
            for _ in range(cnt):
                for i in range(le):
                    ret.append(ret[i] * times)
                times *= bef
            bef = p
            cnt = 1
    ret.sort()
    return ret


n, m = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

ma = max(*A, *B)
ca = [False] * (ma + 2)
cb = [False] * (ma + 2)

for a in A:
    ca[a] = True
for b in B:
    cb[b] = True

if not ca[1] or not cb[1]:
    print(1)
    exit()

for i in range(1, ma + 2):
    if ca[i] or cb[i]:
        continue

    x = i * i
    while 1:
        divs = divisor_lst(x)
        ok = False

        for d in divs:
            a = int(d**0.5)
            while a * a < d:
                a += 1
            while a * a > d:
                a -= 1

            b = int((x // d) ** 0.5)
            while b * b < x // d:
                b += 1
            while b * b > x // d:
                b -= 1

            if (ca[a] and cb[b]) or (ca[b] and cb[a]):
                ok = True
                break

        if ok:
            x += 1
            continue
        else:
            print(x)
            exit()