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}.
import sys
s = input()
K = int(input())

a_list = sorted(set(s))
for i in a_list:
  if K == 1:
    print(i)
    sys.exit()
  p = []
  for j, x in enumerate(s):
    if x == i:
      p.append(s[j:min(j+K,len(s))])
  p.sort()
  print(p)
  t = K
  for j in p:
    if len(j) < K:
      t -= len(j) - 1
    else:
      print(j[0:t])
      sys.exit()
  K = t
import sys
s = input()
K = int(input())

a_list = sorted(set(s))
for i in a_list:
  if K == 1:
    print(i)
    sys.exit()
  p = []
  for j, x in enumerate(s):
    if x == i:
      p.append(s[j:min(j+K,len(s))])
  p.sort()
  t = K
  for j in range(len(p)):
    if j != len(p) - 1:
      if p[j] == p[j+1][0:len(p[j])]:
        continue
    if len(p[j]) < t:
      t -= len(p[j]) - 1
    else:
      print(p[j][0:t])
      sys.exit()
  K = t - 1