from math import lcm
from itertools import cycle

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

t = lcm(N, M)
for i, (a, b) in enumerate(zip(cycle(A), cycle(B))):
    if i == t: break
    if a == b:
        print(i+1)
        exit()

print(-1)