101483: [AtCoder]ABC148 D - Brick Break

Memory Limit:256 MB Time Limit:2 S
Judge Style:Text Compare Creator:
Submit:20 Solved:11

Description

Score : $400$ points

Problem Statement

We have $N$ bricks arranged in a row from left to right.

The $i$-th brick from the left $(1 \leq i \leq N)$ has an integer $a_i$ written on it.

Among them, you can break at most $N-1$ bricks of your choice.

Let us say there are $K$ bricks remaining. Snuke will be satisfied if, for each integer $i$ $(1 \leq i \leq K)$, the $i$-th of those brick from the left has the integer $i$ written on it.

Find the minimum number of bricks you need to break to satisfy Snuke's desire. If his desire is unsatisfiable, print -1 instead.

Constraints

  • All values in input are integers.
  • $1 \leq N \leq 200000$
  • $1 \leq a_i \leq N$

Input

Input is given from Standard Input in the following format:

$N$
$a_1$ $a_2$ $...$ $a_N$

Output

Print the minimum number of bricks that need to be broken to satisfy Snuke's desire, or print -1 if his desire is unsatisfiable.


Sample Input 1

3
2 1 2

Sample Output 1

1

If we break the leftmost brick, the remaining bricks have integers $1$ and $2$ written on them from left to right, in which case Snuke will be satisfied.


Sample Input 2

3
2 2 2

Sample Output 2

-1

In this case, there is no way to break some of the bricks to satisfy Snuke's desire.


Sample Input 3

10
3 1 4 1 5 9 2 6 5 3

Sample Output 3

7

Sample Input 4

1
1

Sample Output 4

0

There may be no need to break the bricks at all.

Input

题意翻译

我们有 $N$ 个砖块从左至右排成一排。 左边第 $i$ 块砖上写着 $a_{i}$ ( $1\le i\le N$ )。 你最多可以打破 $N-1$ 块砖。 假设现在还留下了 $K$ 块砖, 对于每个整数 $i$ ($1\le i \le K$ ), 如果从左数第 $i$ 个上的数字恰好等于 $i$ ,那么 Snuke 就会满意。 寻找最小的打破砖的个数,使满足 Snuke 的愿望。 如果不能,输出 $-1$。 by [djh123456](https://www.luogu.com.cn/user/367575) 。

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