import math
N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
G = math.gcd(N, M)
L = N*M//G
for i in range(L):
    if A[i%N]==B[i%M]:
        print(i+1)
        exit()
print(-1)