def extgcd(a, b):
    if b == 0:
        return 1, 0, a
    q, r = divmod(a, b)
    x, y, d = extgcd(b, r)
    s, t = y, x-q*y
    return s, t, d

def MOD(a, m):
    return (a%m + m)%m;

def CRT_list(b, m):
    # b: list
    # m: list
    # x ≡ bi (mod mi)を満たすx ≡ r (mod lcm(m1*m2..*mn))について
    # r, lcm(m1*m2..*mn)をreturn
    # 解無しの場合は0, -1をreturn
    r, M = 0, 1
    for i in range(len(b)):
        p, q, d = extgcd(M, m[i])
        if (b[i]-r)%d != 0:
            return 0, -1
        temp = (b[i]-r)//d * p % (m[i]//d)
        r += M * temp
        M *= m[i]//d
    return MOD(r, M), M

import math
from functools import reduce
def lcm_base(x, y):
  return (x * y) // math.gcd(x, y)

def lcm_list(numbers):
  return reduce(lcm_base, numbers, 1)

n, m = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

res = float('inf')
P = []
for i, a in enumerate(A):
    for j, b in enumerate(B):
        if a == b:
            if i == j:
                res = min(res, i)
            else:
                P.append((i, j))

for p in P:
    r, M = CRT_list(p, [n, m])
    if M == -1:
        continue
    else:
        res = min(r, res)
if res != float('inf'):
    print(res+1)
else:
    print(-1)