Many Equal Substrings

题目描述： 你有一个字符串t，它由n个字母组成。 定义一个字符串s的子串为s[l...r]，表示从位置l到r构成的一个新的串。 你的目标是构造一个字符串s，使得它的可能长度最小，要求s中存在k个位置i,可以找到k个以i为出发点的子串t。 输入： 第一行输入两个整数n和k，表示t的长度和需要k个子串 第二行输入字符串t 输出： 输出满足条件的长度最小的s。题目保证答案唯一。

You are given a string $ t $ consisting of $ n $ lowercase Latin letters and an integer number $ k $ . Let's define a substring of some string $ s $ with indices from $ l $ to $ r $ as $ s[l \dots r] $ . Your task is to construct such string $ s $ of minimum possible length that there are exactly $ k $ positions $ i $ such that $ s[i \dots i + n - 1] = t $ . In other words, your task is to construct such string $ s $ of minimum possible length that there are exactly $ k $ substrings of $ s $ equal to $ t $ . It is guaranteed that the answer is always unique.

The first line of the input contains two integers $ n $ and $ k $ ( $ 1 \le n, k \le 50 $ ) — the length of the string $ t $ and the number of substrings. The second line of the input contains the string $ t $ consisting of exactly $ n $ lowercase Latin letters.

Print such string $ s $ of minimum possible length that there are exactly $ k $ substrings of $ s $ equal to $ t $ . It is guaranteed that the answer is always unique.

3 4
aba

ababababa

3 2
cat

catcat