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## Challenge:

**Input:** A list of distinct positive integers within the range \$[1, \text{list-size}]\$.

**Output:** An integer: the amount of times the list is [riffle-shuffled](https://upload.wikimedia.org/wikipedia/commons/7/7c/Riffle_shuffle.jpg). For a list, this means the list is split in two halves, and these halves are interleaved (i.e. riffle-shuffling the list `[1,2,3,4,5,6,7,8,9,10]` once would result in `[1,6,2,7,3,8,4,9,5,10]`, so for this challenge the input `[1,6,2,7,3,8,4,9,5,10]` would result in `1`).

## Challenge rules:

- You can assume the list will only contain positive integers in the range \$[1, \text{list-size}]\$ (or \$[0, \text{list-size}-1]\$ if you choose to have 0-indexed input-lists).
- You can assume all input-lists will either be a valid riffle-shuffled list, or a sorted list which isn't shuffled (in which case the output is `0`).
- You can assume the input-list will contain at least three values.

## Step-by-step example:

Input: `[1,3,5,7,9,2,4,6,8]`

Unshuffling it once becomes: `[1,5,9,4,8,3,7,2,6]`, because every even 0-indexed item comes first `[1, ,5, ,9, ,4, ,8]`, and then all odd 0-indexed items after that `[ ,3, ,7, ,2, ,6, ]`. 
The list isn't ordered yet, so we continue:

Unshuffling the list again becomes: `[1,9,8,7,6,5,4,3,2]` 
Again becomes: `[1,8,6,4,2,9,7,5,3]` 
Then: `[1,6,2,7,3,8,4,9,5]` 
And finally: `[1,2,3,4,5,6,7,8,9]`, which is an ordered list, so we're done unshuffling.

We unshuffled the original `[1,3,5,7,9,2,4,6,8]` five times to get to `[1,2,3,4,5,6,7,8,9]`, so the output is `5` in this case.

## General rules:

- This is [tag:code-golf], so shortest answer in bytes wins. 
 Don't let code-golf languages discourage you from posting answers with non-codegolfing languages. Try to come up with an as short as possible answer for 'any' programming language.
- [Standard rules apply](https://codegolf.meta.stackexchange.com/questions/2419/default-for-code-golf-program-function-or-snippet/2422#2422) for your answer with [default I/O rules](https://codegolf.meta.stackexchange.com/questions/2447/default-for-code-golf-input-output-methods/), so you are allowed to use STDIN/STDOUT, functions/method with the proper parameters and return-type, full programs. Your call.
- [Default Loopholes](https://codegolf.meta.stackexchange.com/questions/1061/loopholes-that-are-forbidden-by-default) are forbidden.
- If possible, please add a link with a test for your code (i.e. [TIO](https://tio.run/#)).
- Also, adding an explanation for your answer is highly recommended.

## Test cases:

Input Output

[1,2,3] 0
 [1,2,3,4,5] 0
 [1,3,2] 1
 [1,6,2,7,3,8,4,9,5,10] 1
 [1,3,5,7,2,4,6] 2
 [1,8,6,4,2,9,7,5,3,10] 2
 [1,9,8,7,6,5,4,3,2,10] 3
 [1,5,9,4,8,3,7,2,6,10] 4
 [1,3,5,7,9,2,4,6,8] 5
 [1,6,11,5,10,4,9,3,8,2,7] 6
 [1,10,19,9,18,8,17,7,16,6,15,5,14,4,13,3,12,2,11,20] 10
 [1,3,5,7,9,11,13,15,17,19,2,4,6,8,10,12,14,16,18,20] 17
 [1,141,32,172,63,203,94,234,125,16,156,47,187,78,218,109,249,140,31,171,62,202,93,233,124,15,155,46,186,77,217,108,248,139,30,170,61,201,92,232,123,14,154,45,185,76,216,107,247,138,29,169,60,200,91,231,122,13,153,44,184,75,215,106,246,137,28,168,59,199,90,230,121,12,152,43,183,74,214,105,245,136,27,167,58,198,89,229,120,11,151,42,182,73,213,104,244,135,26,166,57,197,88,228,119,10,150,41,181,72,212,103,243,134,25,165,56,196,87,227,118,9,149,40,180,71,211,102,242,133,24,164,55,195,86,226,117,8,148,39,179,70,210,101,241,132,23,163,54,194,85,225,116,7,147,38,178,69,209,100,240,131,22,162,53,193,84,224,115,6,146,37,177,68,208,99,239,130,21,161,52,192,83,223,114,5,145,36,176,67,207,98,238,129,20,160,51,191,82,222,113,4,144,35,175,66,206,97,237,128,19,159,50,190,81,221,112,3,143,34,174,65,205,96,236,127,18,158,49,189,80,220,111,2,142,33,173,64,204,95,235,126,17,157,48,188,79,219,110,250]
 45

If this is an answer to a challenge…

…Be sure to follow the challenge specification. However, please refrain from exploiting obvious loopholes. Answers abusing any of the standard loopholes are considered invalid. If you think a specification is unclear or underspecified, comment on the question instead.
…Try to optimize your score. For instance, answers to code-golf challenges should attempt to be as short as possible. You can always include a readable version of the code in addition to the competitive one. Explanations of your answer make it more interesting to read and are very much encouraged.
…Include a short header which indicates the language(s) of your code and its score, as defined by the challenge.

More generally…

…Please make sure to answer the question and provide sufficient detail.
…Avoid asking for help, clarification or responding to other answers (use comments instead).

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