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### Kth Substring

### Problem Statement

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`be two distinct strings.

_{1}y_{2}...y_{m}`X`is lexicographically larger than

`Y`if and only if

`Y`is a prefix of

`X`or

`x`where

_{j}> y_{j}`j`is the smallest integer such that

`x`.

_{j}≠ y_{j}### Constraints

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

### Partial Score

`67`points will be awarded as a partial score for passing the test set satisfying`|s|``≤``50`.

### Input

Input is given from Standard Input in the following format:

sK

### Output

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

### Sample Input 1

aba 4

### Sample Output 1

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.

### Sample Input 2

atcoderandatcodeer 5

### Sample Output 2

andat

### Sample Input 3

z 1

### Sample Output 3

z

### Tags

### Subtasks and Limits

Subtask | Score | #TC | Time | Memory | Scoring |
---|---|---|---|---|---|

1 | 67 | 8 | 1s | 256MB | Minimum |

2 | 33 | 16 | 1s | 256MB | Minimum |

3 | 0 | 3 | 1s | 256MB | Minimum |

### Judge Compile Command

g++-7 ans.cpp -o kthsubstring -Wall -static -O2 -lm -m64 -s -w -std=gnu++17 -fmax-errors=512