边界，测试很重要

int cur = 1000;
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            int next = scanner.nextInt();
            if (next > 0 && next + cur < 2000) {
                System.out.println("ok,you can!");
                System.out.println(next +cur);
            } else {
                System.out.println("no you can not !");
            }
        }