You are given a string $s$. Among the different substrings of $s$, print the $K$-th lexicographically smallest one. A substring of $s$ is a string obtained by taking out a non-empty contiguous part in $s$. For example, if $s = \text{ababc}$, `a`, `bab`, and `ababc` are substrings of $s$, while `ac`, `z`, and an empty string are not. Also, we say that substrings are different when they are different as strings. Let $X = x_1x_2\cdots x_n$ and $Y = y_1y_2\cdots y_m$ be two distinct strings. $X$ is lexicographically larger than $Y$ if and only if $Y$ is a prefix of $X$ or $x_j \gt y_j$ where $j$ is the smallest integer such that $x_j \neq y_j$.

Input is given from Standard Input in the following format: > $s$ > $K$ ### Constraints: - $1 \leq |s| \leq 5000$ - $s$ consists of lowercase English letters. - $1 \leq K \leq 5$ - $s$ has at least $K$ different substrings.

Print the $K$-th lexicographically smallest substring of $s$.

**Clarification of the first example:** $s$ has five substrings: `a`, `b`, `ab`, `ba`, and `aba`. Among them, we should print the fourth smallest one, which is `ba`. Note that we do not count `a` twice.