# Rikka with string

Time Limit: 2000/1000 MS (Java/Others)

Memory Limit: 65536/65536 K (Java/Others)

## Description

As we know, Rikka is poor at math. Yuta is worrying about this situation, so he gives Rikka some math tasks to practice. There is one of them:

One day, Yuta got a string which contains n&#8201;letters but Rikka lost it in accident. Now they want to recover the string. Yuta remembers that the string only contains lowercase letters and it is not a palindrome string. Unfortunately he cannot remember some letters. Can you help him recover the string?

It is too difficult for Rikka. Can you help her?

## Input

This problem has multi test cases (no more than $20$). For each test case, The first line contains a number $n(1 \leq n \leq 1000)$. The next line contains an n-length string which only contains lowercase letters and ‘?’ – the place which Yuta is not sure.

## Output

For each test cases print a n-length string – the string you come up with. In the case where more than one string exists, print the lexicographically &#64257;rst one. In the case where no such string exists, output “QwQ”.

## Sample Input

5
a?bb?
3
aaa

## Sample Output

aabba
QwQ

hujie

## Source

BestCoder Round #37 (\$)