Decode the Dreaded Alphabet Cypher™️ This challenge is inspired by one of my other challenges: Pointlessly make your way down the alphabet

That challenge asked you to take a string of text, and for each letter produce a sequence of letters moving down the alphabet to 'a'.

For this challenge I'd like to decode the output of that challenge (minus the line breaks), to find a human-readable string from a much longer human readable string.



Here is some text which has been encoded using the Dreaded Alphabet Cypher™️

hgfedcbaedcbalkjihgfedcbalkjihgfedcbaonmlkjihgfedcba wvutsrqponmlkjihgfedcbaonmlkjihgfedcbarqponmlkjihgfedcbalkjihgfedcbadcba

It consists of descending alphabetical sequences, ending in an 'a'. The first character in each of these sequences is a letter in the decoded text. (A space is still a space).

The challenge


Write code to convert a Dreaded Alphabet Cypher™️ encoded string into a decoded, human-readable string.
No need to validate if it is a Dreaded Alphabet Cypher™️ string, I'm not interested in how it handles invalid input. 
Use any language you please.
Please include a link to an online iterpreter.
The input will only consist of lower-case letters and spaces. No upper cases, punctuation etc.
Code golf, try to write short code, standard loopholes etc.


Test Cases

Input:

hgfedcbaedcbalkjihgfedcbalkjihgfedcbaonmlkjihgfedcba wvutsrqponmlkjihgfedcbaonmlkjihgfedcbarqponmlkjihgfedcbalkjihgfedcbadcba


Output:

hello world




Input: 

abacbadcbaedcbafedcbagfedcbahgfedcbaihgfedcbajihgfedcbakjihgfedcbalkjihgfedcbamlkjihgfedcbanmlkjihgfedcbaonmlkjihgfedcbaponmlkjihgfedcbaqponmlkjihgfedcbarqponmlkjihgfedcbasrqponmlkjihgfedcbatsrqponmlkjihgfedcbautsrqponmlkjihgfedcbavutsrqponmlkjihgfedcbawvutsrqponmlkjihgfedcbaxwvutsrqponmlkjihgfedcbayxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba


Output:

abcdefghijklmnopqrstuvwxyz




(beware the multiple a's)

Input:

aarqponmlkjihgfedcbaonmlkjihgfedcbanmlkjihgfedcba a aarqponmlkjihgfedcbaonmlkjihgfedcbanmlkjihgfedcbasrqponmlkjihgfedcbaonmlkjihgfedcbanmlkjihgfedcba hgfedcbaasrqponmlkjihgfedcba anmlkjihgfedcba aarqponmlkjihgfedcbadcbavutsrqponmlkjihgfedcbaarqponmlkjihgfedcbakjihgfedcba


Output:

aaron a aaronson has an aardvark




Input:

hgfedcbaaponmlkjihgfedcbaponmlkjihgfedcbayxwvutsrqponmlkjihgfedcba gfedcbaonmlkjihgfedcbalkjihgfedcbafedcbaihgfedcbanmlkjihgfedcbagfedcba


Output (is a secret, shh)
JavaScript (ES9),  37 33  26 bytes
Returns an array of characters.
Either a negative look-behind:

s=&gt;s.match(/(?&lt;![b-z])./g)

Try it online!
Or a positive look-behind:
s=&gt;s.match(/(?&lt;=a| |^)./g)

Try it online!

25 bytes
If the input is guaranteed not to contain leading or double spaces (or we're allowed to remove and collapse them respectively), the positive look-behind can be made 1 byte shorter:

s=&gt;s.match(/(?&lt;=a|\b)./g)

Try it online!