import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
sys.setrecursionlimit(10**7)
yes = lambda :print("yes");Yes = lambda :print("Yes")
no = lambda :print("no");No = lambda :print("No")
#######################################################################

n,m = na()
a = na()
b = na()

for i in range(n*m):
    if a[i%n]==b[i%m]:
        print(i+1)
        exit()
print(-1)