2017 Winter Waterloo Local ACM Contest, Problem B

Vera is learning about the longest common subsequence problem.

A string is a (possibly empty) sequence of lowercase letters. A subsequence of a string ~S~ is a string obtained by deleting some letters of ~S~ (possibly none or all). For example vra, a,  (empty string), and vera are all subsequences of vera. The longest common subsequence (LCS) of two strings ~A~ and ~B~ is a string that is a subsequence of both ~A~ and ~B~ that has the maximum length among all strings that are a subsequence of both ~A~ and ~B~. There could be multiple LCS for two given strings. For example, a LCS of vera and eats is ea.

For homework, she was given two strings ~A~, ~B~, both of length ~N~ and she had to determine the length of the LCS of ~A~ and ~B~. She determined the answer to be ~K~ but lost ~B~. Given ~A~ and ~K~, help her find a possible value of ~B~. It is possible that Vera may have made a mistake and no such ~B~ exists, in that case output WRONGANSWER.

Constraints

• ~1 \le N \le 2000~
• ~0 \le K \le 2000~
• ~N~, ~K~ are integers
• ~A~ consists of ~N~ lowercase letters

Input Specification

The input will be in the format:

~N~ ~K~

~A~

Output Specification

Output one line consisting of the string ~B~ of ~N~ lowercase letters, or WRONGANSWER if no ~B~ is valid. If there are multiple correct ~B~ output any of them.

Sample Input 1

4 2
vera

Sample Output 1

eats

Explanation of Sample Output 1

Another possible answer is uber.

Sample Input 2

4 5
vera

Sample Output 2

WRONGANSWER