Phone Numbers
Description
And where the are the phone numbers?
You are given a string s consisting of lowercase English letters and an integer k. Find the lexicographically smallest string t of length k, such that its set of letters is a subset of the set of letters of s and s is lexicographically smaller than t.
It's guaranteed that the answer exists.
Note that the set of letters is a set, not a multiset. For example, the set of letters of abadaba is {a, b, d}.
String p is lexicographically smaller than string q, if p is a prefix of q, is not equal to q or there exists i, such that pi < qi and for all j < i it is satisfied that pj = qj. For example, abc is lexicographically smaller than abcd , abd is lexicographically smaller than abec, afa is not lexicographically smaller than ab and a is not lexicographically smaller than a.
The first line of input contains two space separated integers n and k (1 ≤ n, k ≤ 100 000) — the length of s and the required length of t.
The second line of input contains the string s consisting of n lowercase English letters.
Output the string t conforming to the requirements above.
It's guaranteed that the answer exists.
Input
The first line of input contains two space separated integers n and k (1 ≤ n, k ≤ 100 000) — the length of s and the required length of t.
The second line of input contains the string s consisting of n lowercase English letters.
Output
Output the string t conforming to the requirements above.
It's guaranteed that the answer exists.
Samples
3 3
abc
aca
3 2
abc
ac
3 3
ayy
yaa
2 3
ba
baa
Note
In the first example the list of strings t of length 3, such that the set of letters of t is a subset of letters of s is as follows: aaa, aab, aac, aba, abb, abc, aca, acb, .... Among them, those are lexicographically greater than abc: aca, acb, .... Out of those the lexicographically smallest is aca.