from math import gcd

def solve():
    n, m = map(int, input().split())
    A = list(map(int, input().split()))
    B = list(map(int, input().split()))
    
    i = j = 0
    x = 1
    ans = -1
    for _ in range(n * m // gcd(n, m)):
        if A[i] == B[j]:
            ans = x
            break
        x += 1
        if i == n - 1:
            i = 0
        else:
            i += 1
        if j == m - 1:
            j = 0
        else:
            j += 1
        
    print(ans)
solve()