import sys
import math

def main():
    input = sys.stdin.read().split()
    ptr = 0
    N, M = int(input[ptr]), int(input[ptr+1])
    ptr +=2
    A = list(map(int, input[ptr:ptr+N]))
    ptr +=N
    B = list(map(int, input[ptr:ptr+M]))
    ptr +=M

    def is_in(x, arr):
        left = 0
        right = len(arr) -1
        res = -1
        while left <= right:
            mid = (left + right) //2
            a = arr[mid]
            a_sq = a * a
            if a_sq <= x:
                res = mid
                left = mid +1
            else:
                right = mid -1
        if res == -1:
            return False
        return x < (arr[res] +1) **2

    k = 1
    while True:
        max_d = int(math.isqrt(k))
        found = False
        for d in range(1, max_d +1):
            if k % d !=0:
                continue
            e = k // d
            # Check d in A and e in B
            if is_in(d, A) and is_in(e, B):
                found = True
                break
            # Check e in A and d in B
            if d != e and is_in(e, A) and is_in(d, B):
                found = True
                break
        if not found:
            print(k)
            return
        k +=1

if __name__ == "__main__":
    main()