N,M = map(int,input().split())
A = list(map(int,input().split()))
B = list(map(int,input().split()))
flg = False
ans = float('inf')
for i in range(N):
  for j in range(M):
    if A[i] == B[j]:
      num = 0
      while num <= min(N,M):
        if (num*N+i-j)%M == 0:
          flg = True
          ans = min(ans,num*N+i+1)
          break
        num += 1

if flg:
  print(ans)
else:
  print(-1)