CF1630C.Paint the Middle

普及/提高-

通过率：0%

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题目描述

You are given $n$ elements numbered from $1$ to $n$ , the element $i$ has value $a_i$ and color $c_i$ , initially, $c_i = 0$ for all $i$ .

The following operation can be applied:

Select three elements $i$ , $j$ and $k$ ( $1 \leq i < j < k \leq n$ ), such that $c_i$ , $c_j$ and $c_k$ are all equal to $0$ and $a_i = a_k$ , then set $c_j = 1$ .

Find the maximum value of $\sum\limits_{i=1}^n{c_i}$ that can be obtained after applying the given operation any number of times.

输入格式

The first line contains an integer $n$ ( $3 \leq n \leq 2 \cdot 10^5$ ) — the number of elements.

The second line consists of $n$ integers $a_1, a_2, \dots, a_n$ ( $1 \leq a_i \leq n$ ), where $a_i$ is the value of the $i$ -th element.

输出格式

Print a single integer in a line — the maximum value of $\sum\limits_{i=1}^n{c_i}$ that can be obtained after applying the given operation any number of times.

输入输出样例

输入#1
```
7
1 2 1 2 7 4 7
```
输出#1
```
2
```
输入#2
```
13
1 2 3 2 1 3 3 4 5 5 5 4 7
```
输出#2
```
7
```

说明/提示

In the first test, it is possible to apply the following operations in order:

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