CF30E Tricky and Clever Password

In his very young years the hero of our story, king Copa, decided that his private data was hidden not enough securely, what is unacceptable for the king. That's why he invented tricky and clever password (later he learned that his password is a palindrome of odd length), and coded all his data using it. Copa is afraid to forget his password, so he decided to write it on a piece of paper. He is aware that it is insecure to keep password in such way, so he decided to cipher it the following way: he cut $ x $ characters from the start of his password and from the end of it ( $ x $ can be $ 0 $ , and $ 2x $ is strictly less than the password length). He obtained 3 parts of the password. Let's call it $ \mathit{prefix} $ , $ \mathit{middle} $ and $ \mathit{suffix} $ correspondingly, both $ \mathit{prefix} $ and $ \mathit{suffix} $ having equal length and $ \mathit{middle} $ always having odd length. From these parts he made a string $ A+\mathit{prefix}+B+\mathit{middle}+C+\mathit{suffix} $ , where $ A $ , $ B $ and $ C $ are some (possibly empty) strings invented by Copa, and « $ + $ » means concatenation. Many years have passed, and just yesterday the king Copa found the piece of paper where his ciphered password was written. The password, as well as the strings $ A $ , $ B $ and $ C $ , was completely forgotten by Copa, so he asks you to find a password of maximum possible length, which could be invented, ciphered and written by Copa.

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