N,M = map(int,input().split())
A = list(map(int,input().split()))
B = list(map(int,input().split()))
import sys
ans = 10 ** 10
for j in range(M):
    for i in range(N):
        k = (j * N + i) % M
        if A[i] == B[k]:
            print(j * N + i + 1)
            exit()
print(-1)