CF1840A Cipher Shifer

There is a string $ a $ (unknown to you), consisting of lowercase Latin letters, encrypted according to the following rule into string $ s $ : - after each character of string $ a $ , an arbitrary (possibly zero) number of any lowercase Latin letters, different from the character itself, is added; - after each such addition, the character that we supplemented is added. You are given string $ s $ , and you need to output the initial string $ a $ . In other words, you need to decrypt string $ s $ . Note that each string encrypted in this way is decrypted uniquely.

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In the first encrypted message, the letter $ a $ is encrypted as $ aba $ , and the letter $ c $ is encrypted as $ cabac $ . In the second encrypted message, only one letter $ q $ is encrypted as $ qzxcq $ . In the third encrypted message, zero characters are added to each letter.