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 C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main()
{
	char str[5005];
	int k;
	int len;
	char dict[25005][6] = {};
	int cnt;
	int ans_indx;

	scanf("%s", str);
	scanf("%d", &k);

	len = strlen(str);

	cnt = 0;
	for (int i = 0; i < k; i++) {
		for (int j = 0; j + i < len; j++) {

			for (int ii = j; ii <= j + i; ii++) {
				dict[cnt][ii - j] = str[ii];
			}
			cnt++;

		}
	}

	qsort(*dict, cnt, 6, (int (*)(const void *, const void *))strcmp);

	ans_indx = -1;
	int ccnt = 0;
	while (ccnt < k) {
		if (strcmp(dict[ans_indx], dict[ans_indx + 1])) { 
			ccnt++;
		}

		ans_indx++;
	}

	printf("%s\n", dict[ans_indx]);

	return 0;
}