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 Pascal (FPC 2.6.2) (judge verdict: Accepted)

{$mode objfpc}
program C;
uses
  classes, math;

var
  S: AnsiString;
  k: Integer;
  i, j: Integer;
  AllSubStr: TStringList;

begin
  ReadLn(S);
  ReadLn(k);

  AllSubStr := TStringList.Create;

  for i := 1 to Length(S) do 
    for j := 1 to Min(k, Length(S) - i + 1) do
      AllSubStr.Add(Copy(S, i, j));
  AllSubStr.Sort;
 
  i := 0;
  for j := 0 to AllSubStr.Count - 1 do 
    if AllSubStr[i] <> AllSubStr[j] then
    begin
      Inc(i);
      AllSubStr[i] := AllSubStr[j];
    end;
  {
  for j := 0 to i do 
    WriteLn(AllSubStr[j]);
  }
  WriteLn(AllSubStr[k - 1]);
  
end.