Gacha

Problem Source

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Problem Description

There are $n$ cards, each with a string $s_i$ on it. Now you must select $k$ of these cards so that, among all selection schemes, concatenating the $k$ cards gives a string with the lexicographically smallest value (see samples for details).

Input Format

The first line contains two integers $n, k$ ($1 \le k \le n \le 50$).

The next $n$ lines each contain a string $s_i$ ($1 \le |s_i| \le 50$).

Output Format

Output one string: the lexicographically smallest string among all schemes that select $k$ cards.

Sample Input 1

4 3
ode
zaaa
r
atc

Sample Output 1

atcoder

Sample Input 2

5 2
z
z
zzz
z
zzzzzz

Sample Output 2

zz