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 Python (3.8.2) (judge verdict: Accepted)

s = str(input())
K = int(input())
L = []
M = []
con = 0
for i in s:
  L.append(i)
L = list(set(L))
L.sort()
for j in range(len(s)):
    if s[j] == L[0]:
      for k in range(1,6):
        if j + k >=len(s):
          M.append(s[j:])
          break
        else:
          M.append(s[j:j+k])
if len(L) != 1:
  for l in range(len(s)):
    if s[l] == L[1]:
      for m in range(1,6):
        if l + m >= len(s):
          M.append(s[l:])
          break
        else:
          M.append(s[l:l+m]) 
if len(M) < K:
  for n in range(len(s)):
    if s[n] == L[2]:
      for o in range(1,6):
        if n + o >=len(s):
          M.append(s[n:])
          break
        else:
          M.append(s[n:n+o])
M = list(set(M))
M.sort()
print(M[K - 1])