from collections import defaultdict

def Ext_gcd(a,b): #GCD,x,yを返す。ax +by = GCD
  if b == 0:
    return (a,1,0)
  g,y,x = Ext_gcd(b,a%b)
  y -= a//b*x
  return (g,x,y)

def ChiniseRem(b1,m1,b2,m2):
  g,p,q = Ext_gcd(m1,m2)
  if (b1-b2)%g != 0:
    return (0,-1)
  m = m1*m2//g
  temp = (b2-b1)//g*p%(m2//g)
  x = (b1 + m1*temp)%m
  return (x,m)

def main():
    N,M = map(int,input().split()); INF = float("inf")
    A = list(map(int,input().split()))
    B = list(map(int,input().split()))
    for i in range(N*M):
        a = A[i%N]
        b = B[i%M]
        if a == b:
            print(i+1)
            exit()
    print(-1)
    exit()
    adic = defaultdict(list)
    bdic = defaultdict(list)
    for i,a in enumerate(A):
        adic[a].append(i)
    for i,b in enumerate(B):
        bdic[b].append(i)
    #print(adic)
    #print(bdic)
    ans = INF
    for a in adic:
        if a not in bdic: continue
        for p in adic[a]:
            for q in bdic[a]:
                #print(a,p,q)
                x,m = ChiniseRem(p,N,q,M)
                ans = min(ans, x)
    if ans == INF:
        print(-1)
    else:
        print(ans+1)

if __name__ == '__main__':
    main()