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 = [i,j,abs(A[i]-B[j])]
        flg = True
      else:
        if abs(A[i]-B[j]) < p[2]:
          p = [i,j,abs(A[i]-B[j])]
if flg:
  ans = float('inf')
  a,b = p[0],p[1]
  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)