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_{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 $x_{j} \neq y_{j}$.

Input

Input is given from Standard Input in the following format:
s
K

Output

Print the K-th lexicographically smallest substring of K.

Constraints

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

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

见题面 Input 部分

见题面 Output 部分