from math import gcd
N, M = map(int, input().split())

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

A = A*(M//g)
B = B*(N//g)

for i in range(len(A)):
    if A[i] == B[i]:
        print(i+1)
        exit(0)

print(-1)