kthsubstring

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 = x₁x₂...x_n and Y = y₁y₂...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 ≠ 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:

s
K

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