CF452F.Permutation

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题目描述

You are given a permutation of numbers from $1$ to $n$ . Determine whether there's a pair of integers $a,b$ $(1<=a,b<=n; a≠b)$ such that the element (note, that it is usual division, not integer one) is between $a$ and $b$ in this permutation.

输入格式

First line consists of a single integer $n$ ( $1<=n<=300000$ ) — the size of permutation.

Second line contains $n$ integers — the permutation itself.

输出格式

Print "YES", if such a pair exists, "NO" otherwise (in both cases without quotes, the answer is case insensitive).

输入输出样例

输入#1
```
4
1 3 4 2
```
输出#1
```
NO
```
输入#2
```
5
1 5 2 4 3
```
输出#2
```
YES
```

说明/提示

In the second example $2$ is between $1$ and $3$ . Additionally $4$ is between $3$ and $5$ .

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