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...xn and Y = y1y2...ym be two distinct strings. X is lexicographically larger than Y if and only if Y is a prefix of X or xj > yj where j is the smallest integer such that xj ≠ yj.

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

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Compile Errors


							
Time Limit: 2 Seconds
Memory Limit: 256MB
No. of ACs: 10
Your best score: 0
Source: ARC 097

Subtask Score
1 67
2 33
3 0