B. Hate "A"

题目链接
Bob has a string s consisting of lowercase English letters. He defines s′ to be the string after removing all “a” characters from s (keeping all other characters in the same order). He then generates a new string t by concatenating s and s′. In other words, t=s+s′ (look at notes for an example).

You are given a string t. Your task is to find some s that Bob could have used to generate t. It can be shown that if an answer exists, it will be unique.

Input
The first line of input contains a string t (1≤|t|≤10⁵) consisting of lowercase English letters.

Output
Print a string s that could have generated t. It can be shown if an answer exists, it is unique. If no string exists, print “

标签：pre,suf,string,str,output,input,Hate
来源： https://blog.csdn.net/qq_37708702/article/details/90081757