N,M=map(int,input().split())
A=list(map(int,input().split()))
B=list(map(int,input().split()))
L=N*M
X=[A[i%N] for i in range(L)]
Y=[B[i%M] for i in range(L)]
for i in range(L):
  if X[i]==Y[i]:
    print(i+1)
    exit()
print(-1)