def main():
    import sys
    input=sys.stdin.buffer.readline
    n,m=map(int,input().split())
    a=list(map(int,input().split()))*m
    b=list(map(int,input().split()))*n
    for i in range(n*m):
        if a[i]==b[i]:
            print(i+1)
            return
    print(-1)
main()