Contest: Task: Related: TaskB

Score : $300$ points

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 $s$ $=$ `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 $X = x_{1}x_{2}...x_{n}$ and $Y = y_{1}y_{2}...y_{m}$ be two distinct strings. $X$ is lexicographically larger than $Y$ if and only if $Y$ is a prefix of $X$ or $x_{j} > y_{j}$ where $j$ is the smallest integer such that $x_{j} \neq y_{j}$.

- $1$ $≤$ $|s|$ $≤$ $5000$
- $s$ consists of lowercase English letters.
- $1$ $≤$ $K$ $≤$ $5$
- $s$ has at least $K$ different substrings.

- $200$ points will be awarded as a partial score for passing the test set satisfying $|s|$ $≤$ $50$.

Input is given from Standard Input in the following format:

$s$ $K$

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

aba 4

b

$s$ has five substrings: `a`

, `b`

, `ab`

, `ba`

and `aba`

.
Among them, we should print the fourth smallest one, `b`

.
Note that we do not count `a`

twice.

atcoderandatcodeer 5

andat

z 1

z