def main():
  from sys import stdin
  readline=stdin.readline
  n, m = map(int, readline().split())
  A = list(map(int, readline().split()))
  B = list(map(int, readline().split()))
  A = A*m
  B = B*n
  for i in range(n*m):
    if A[i] == B[i]:
      print(i+1)
      break
  else:
    print(-1)
main()