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)

var s:ansistring;
    a:array[0..100000]of string;
    i,j:longint;
    n,k:longint;
    num:longint;
    s1:string;
procedure qs(l,r:longint);
var i,j:longint;
    m,t:string;
begin
  i:=l;
  j:=r;
  m:=a[(l+r)>>1];
  repeat
    while a[i]<m do inc(i);
    while a[j]>m do dec(j);
    if i<=j then
    begin
      t:=a[i];a[i]:=a[j];a[j]:=t;
      inc(i);
      dec(j);
    end;
  until i>j;
  if l<j then qs(l,j);
  if i<r then qs(i,r);
end;
begin
  readln(s);
  n:=length(s);
  readln(k);
  for i:=1 to n do
  begin
    s1:='';
    for j:=0 to k-1 do
    if i+j<=n then
    begin
      s1:=s1+s[i+j];
      inc(num);
      a[num]:=s1;
    end;
  end;
  qs(1,num);
  for i:=1 to num do
  begin
    if a[i]<>a[i-1] then dec(k);
    if k=0 then
    begin
      writeln(a[i]);
      exit;
    end;
  end;
end.