CF1876C.Autosynthesis

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.

Chaneka 写下一个包含 $n$ 个正整数元素的数组 $a$。初始时，所有元素均未被圈出。在一次操作中，Chaneka 可以圈出一个元素。同一个元素可以被多次圈出。

在完成所有操作后，Chaneka 构造序列 $r$，它由数组 $a$ 中所有未被圈出的元素按其下标顺序组成。

Chaneka 还构造另一个序列 $p$，其长度等于执行的操作次数，且 $p_i$ 表示第 $i$ 次操作中被圈出元素的下标。

Chaneka 希望执行若干次操作，使得序列 $r$ 等于序列 $p$。请帮她实现这一目标，或判断这是不可能的！注意：若存在多种解法，输出任意一种即可。

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 $a_1,a_2,a_3,\ldots,a_n$ ($1\leq a_i\leq n$).

第一行包含一个整数 $n$（$1 \leq n \leq 2\cdot10^5$）—— 数组 $a$ 的大小。

第二行包含 $n$ 个整数 $a_1,a_2,a_3,\ldots,a_n$（$1\leq a_i\leq n$）。

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.

如果无法实现，则输出一行，包含 $-1$。

否则，输出包含两行。第一行包含一个整数 $z$，表示执行的操作次数。第二行包含 $z$ 个整数，其中第 $i$ 个整数表示第 $i$ 次操作中被圈出的元素的索引。若存在多种解，输出任意一种即可。

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.

在第一个例子中，按照示例输出所描述的操作，得到以下结果：

• 元素 $a_2$ 被圈出 $1$ 次。
• 元素 $a_3$ 被圈出 $2$ 次。
• 未被圈出的元素（按其下标升序排列）为 $a_1$、$a_4$ 和 $a_5$。因此 $r=[3,2,3]$。
• $p=[3,2,3]$

因此，$r=p$。

在第二个例子中，这是不可能的。