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 Fortran (gfortran v4.8.4) (judge verdict: Time Limit Exceeded)

program arc097_a
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int32):: n,i,j,l,r,k
    character(5000):: s, s_list(5),subs

    read*, s
    read*, k
    s_list(:) = ''
    do i=1,5
        do j=1,5000
            s_list(i) = trim(s_list(i)) // 'z'
        end do
    end do
    n = len_trim(s)
    
    do l=1,n
        do r=l,n
            subs = s(l:r)
            do i=1,5
                if (subs == s_list(i)) exit
                if (subs < s_list(i)) call swap(subs, s_list(i))
            end do
        end do
    end do
    print'(a)', trim(s_list(k))
contains
    subroutine swap(s1,s2)
        character(5000):: s1,s2,tmp
        tmp=s1; s1=s2; s2=tmp
    end subroutine

end program arc097_a