Autosynthesis

给定一个 $n$ 个数的序列 $a$。你可以进行若干次操作，每次操作可以在一个数 $a_i$ 上画圈。 你需要满足以下要求：设你的操作次数为 $k$，$p_{1\cdots k}$ 为你每次操作时画圈的 **下标**，你需要满足没有画圈的数字个数 **恰好为 $k$**，且这些数字组成的子序列 $b_{1\cdots k}$ 与 $p_{1\cdots k}$ 相等。 请你构造一组方案。如果不存在合法方案，输出 `-1`。 $1\le n\le 4\times 10^5,1\le a_i\le n$。

Chaneka writes down an array $ a $ of $ n $ positive integer elements. Initially, all elements are not circled. In one operation, Chaneka can circle an element. It is possible to circle the same element more than once. After doing all operations, Chaneka makes a sequence $ r $ consisting of all uncircled elements of $ a $ following the order of their indices. Chaneka also makes another sequence $ p $ such that its length is equal to the number of operations performed and $ p_i $ is the index of the element that is circled in the $ i $ -th operation. Chaneka wants to do several operations such that sequence $ r $ is equal to sequence $ p $ . Help her achieve this, or report if it is impossible! Note that if there are multiple solutions, you can print any of them.

The first line contains a single integer $ n $ ( $ 1 \leq n \leq 2\cdot10^5 $ ) — the size of array $ a $ . The second line contains $ n $ integers $ a_1,a_2,a_3,\ldots,a_n $ ( $ 1\leq a_i\leq n $ ).

A single line containing $ -1 $ if it is impossible. Otherwise, the output consists of two lines. The first line contains an integer $ z $ representing the number of operations performed. The second line contains $ z $ integers, the $ i $ -th integer represents the index of the element circled in the $ i $ -th operation. If there are multiple solutions, you can print any of them.

5
3 4 2 2 3

3
3 2 3

3
1 2 3

-1

In the first example, doing the operations like the example output gives the following results: - Element $ a_2 $ gets circled $ 1 $ time. - Element $ a_3 $ gets circled $ 2 $ times. - The uncircled elements (ordered by their indices) are $ a_1 $ , $ a_4 $ , and $ a_5 $ . So $ r=[3,2,3] $ . - $ p=[3,2,3] $ Therefore, $ r=p $ . In the second example, it is impossible.