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.

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.

Examples

Input

3 3
abc


Output

aca


Input

3 2
abc


Output

ac


Input

3 3
ayy


Output

yaa


Input

2 3
ba


Output

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.
import jdk.nashorn.internal.runtime.regexp.joni.encoding.CharacterType;

import java.io.*;
import java.util.*;
import java.io.IOException;
import java.io.InputStream;

import static java.lang.Math.ceil;

public class Main {
    public static void main(String[] args) {

        File file = new File("in.txt");
        File fileOut = new File("out.txt");
        InputStream inputStream = null;
        OutputStream outputStream = null;
        // try {inputStream= new FileInputStream(file);} catch (FileNotFoundException ex){return;};
//        try {outputStream= new FileOutputStream(fileOut);} catch (FileNotFoundException ex){return;};
        inputStream = System.in;
        outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    }


}

class Task {



    public void solve(int testNumber, InputReader in, PrintWriter out) {
        Integer n = in.nextInt();
        Integer k = in.nextInt();
        String s = in.next();
        NavigableSet<Character> sch = new TreeSet<>();
        for(int i=0; i<n; i++){
            sch.add(s.charAt(i));
        }


        if(k>n){
            StringBuilder sb = new StringBuilder();
            sb.append(s);
            Character min = sch.pollFirst();
            for(int i=0; i<k-n; i++){
                sb.append(min);
            }
            out.println(sb.toString());
            return;
        }

        char[] result = new char[k];
        Character max = sch.pollLast();
        sch.add(max);
        Integer last = lastRaisable(s, k-1, max);

        for(int i=0; i<last; i++){
            result[i] = s.charAt(i);
        }
        result[last] = sch.higher(s.charAt(last));
        sch.add(result[last]);
        Character min = sch.pollFirst();
        for(int i=last+1; i<k; i++){
            result[i] = min;
        }
        StringBuilder sb = new StringBuilder();
        for(char ch : result){
            sb.append(ch);
        }
        out.println(sb.toString());





    }


    public Integer lastRaisable(String s, Integer fromPos, Character ch){
        for(int i=fromPos; i>=0; i--){
            if(s.charAt(i) < ch){
                return i;
            }
        }
        return  null;

    }



}

class InputReader {
    public BufferedReader reader;
    public StringTokenizer tokenizer;

    public InputReader(InputStream stream) {
        reader = new BufferedReader(new InputStreamReader(stream), 32768);
        tokenizer = null;
    }

    public String next() {
        while (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }

    public String nextLine(){
        try {
            return reader.readLine();
        } catch (IOException e){
            throw new RuntimeException(e);
        }
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }
    public long nextLong() { return Long.parseLong(next()); }

}



class Pair<F, S> {
    public final F first;
    public final S second;




    public Pair(F first, S second) {
        this.first = first;
        this.second = second;
    }

    @Override
    public boolean equals(Object o) {
        if (!(o instanceof Pair)) {
            return false;
        }
        Pair<?, ?> p = (Pair<?, ?>) o;
        return Objects.equals(p.first, first) && Objects.equals(p.second, second);
    }

    @Override
    public int hashCode() {
        return (first == null ? 0 : first.hashCode()) ^ (second == null ? 0 : second.hashCode());
    }

    @Override
    public String toString() {
        return "(" + first + ", " + second + ')';
    }
}

class IntPair extends Pair<Integer, Integer>{
    public IntPair(Integer first, Integer second){
        super(first, second);
    }
}

class LPair extends Pair<Long, Long>{
    public LPair(Long first, Long second){
        super(first, second);
    }
}