N,M = map(int,input().split())
A = list(map(int,input().split()))
B = list(map(int,input().split()))
flg = False
p = []
for i in range(N):
  for j in range(M):
    if A[i] == B[j]:
      if not flg:
        p.append([i,j])
        flg = True
      else:
        if abs(i-j) == abs(p[-1][0]-p[-1][1]):
          p.append([i,j])
        elif abs(i-j) < abs(p[-1][0]-p[-1][1]):
          p = [[i,j]]
        else:
          pass
if flg:
  ans = float('inf')
  for a,b in p:
    for n in range(N*M+1):
      m = (N*n+a-b)/M
      if m.is_integer():
        ans = min(ans,N*n+a+1)
  print(ans)
else:
  print(-1)