im still unable to do this https://mirror.codeforces.com/problemset/problem/1146/B

someone said i need to explain my solution https://pastebin.com/f4eze85S

what i want to do:

stripg all 'a'

and then check the new string if first half is the same as second half like bcbc its the same

if yes then erase occurence in input string like abc and the occurence is bc then it should print a.