Problem:
Score : 300 points

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}.

Constraints

1 ≤ |s| ≤ 5000

s consists of lowercase English letters.

1 ≤ K ≤ 5

s has at least K different substrings.

Partial Score

200 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

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Runtime Error)

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Scanner;

class Main{

	public static void main(String[] args) {


		Scanner scan = new Scanner(System.in);
		String s = scan.next();
		int x = scan.nextInt();
		ArrayList<String> list  = new ArrayList<String>();

		if(s.length() == 1){
			System.out.println(s);

		}else{
			for(int i =0; i < s.length()-1;i++){
				for(int j = i+1;j <= s.length();j++){
					if(j -i > 5){
						break;	
					}
					
					list.add(s.substring(i, j));
				}
			}
			ArrayList<String> xlist = new ArrayList<String>(new HashSet<>(list));
			Collections.sort(xlist);
			System.out.println(xlist.get(x-1));



		}
	}





}