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A9664 | $Little Pony and Sort by Shift$

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内存限制256MB

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题目描述

One day, Twilight Sparkle is interested in how to sort a sequence of integers $a_{1},a_{2},...,a_{n}$ in non-decreasing order. Being a young unicorn, the only operation she can perform is a unit shift. That is, she can move the last element of the sequence to its beginning: $a_{1},a_{2},...,a_{n}→a_{n},a_{1},a_{2},...,a_{n-1}.$ Help Twilight Sparkle to calculate: what is the minimum number of operations that she needs to sort the sequence?

输入格式

The first line contains an integer $n$ $(2<=n<=10^{5})$ . The second line contains $n$ integer numbers $a_{1},a_{2},...,a_{n}$ $(1<=a_{i}<=10^{5})$ .

输出格式

If it's impossible to sort the sequence output -1. Otherwise output the minimum number of operations Twilight Sparkle needs to sort it.

输入输出样例

输入 #1

2
2 1

输出 #1

输入 #2

3
1 3 2

输出 #2

-1

输入 #3

2
1 2

输出 #3

C++ 编辑器

输入

输出