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 java.util.*;
import java.io.*;

public class C
{

    Reader in;
    PrintWriter out;
    int i = 0, j = 0;
    void solve()
    {
        
        //START// 
        int n = in.nextInt(), k = in.nextInt();
        TreeSet<Character> c = new TreeSet<Character>();
        String s = in.next();
        for (char cur = 'a'; cur <= 'z'; cur++)
        {
            if (s.indexOf(cur) != -1)
                c.add(new Character(cur));
        }
        char highest = c.last().charValue();
        char lowest = c.first().charValue();
        char[] sol;
        if (k > n)
        {
            out.print(s);
            for (i = 0; i < (k-n); i++)
                out.print(lowest);
            out.println();
            return;
        }
        sol = s.substring(0,k).toCharArray();
        int notHighInd=0;
        for (i = sol.length-1; i>=0;i--)
        {
            if (sol[i] != highest)
            {
                notHighInd = i;
                break;
            }
        }
        sol[notHighInd] = c.higher((Character)sol[notHighInd]).charValue();
        for (i = notHighInd+1; i < sol.length; i++)
            sol[i]=lowest;
        out.println(new String(sol));







        //END
        
    }
    void runIO()
    {
        in = new Reader();
        out = new PrintWriter(System.out, false);
        solve();
        out.close();
    }

    public static void main(String[] args)
    {
        new C().runIO();
    }


    // input/output
    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        

        public final String next()
        {
            int c = read();
            while (isSpaceChar(c))
            {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do
            {
                res.append((char) c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        private boolean isSpaceChar(int c)
        {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public int nextInt()
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong()
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble()
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (c == '.')
                while ((c = read()) >= '0' && c <= '9')
                    ret += (c - '0') / (div *= 10);
            if (neg)
                return -ret;
            return ret;
        }

        public int[] readIntArray(int size)
        {
            int[] arr = new int[size];
            for (int i = 0; i < size; i++)
                arr[i] = nextInt();
            return arr;
        }

        public long[] readLongArray(int size)
        {
            long[] arr = new long[size];
            for (int i = 0; i < size; i++)
                arr[i] = nextInt();
            return arr;
        }

        private void fillBuffer()
        {
            try
            {
                bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            }
            catch (IOException e)
            {

            }
            
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read()
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }
    }
}
