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.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.io.IOException;
import java.util.TreeSet;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Pradyumn
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        FastReader in = new FastReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC {
        public void solve(int testNumber, FastReader in, PrintWriter out) {
            Debug debug = new Debug(out);
            int n = in.nextInt();
            int K = in.nextInt();
            char[] s = in.nextString().toCharArray();
            char[] t = null;
            char minChar = s[0];
            for (char ss : s) minChar = (char) Math.min(ss, minChar);
            if (n < K) {
                t = s.clone();
                t = Arrays.copyOf(t, K);
                for (int i = s.length; i < K; ++i) t[i] = minChar;
            } else if (n == K) {
                t = s.clone();
                t = Arrays.copyOf(t, K);
                TreeSet<Character> set = new TreeSet<>();
                for (char ss : s) set.add(ss);
                boolean flag = false;
                for (int i = K - 1; i >= 0; --i) {
                    set.remove(t[i]);
                    Character ss = set.higher(t[i]);
                    set.add(t[i]);

                    if (ss == null) continue;
                    t[i] = ss;

                    for (int j = i + 1; j < K; ++j) t[j] = set.first();
                    flag = true;
                    break;
                }
                if (!flag) throw new RuntimeException();
            } else if (n > K) {
                t = new char[K];
                ArrayUtils.fill(t, minChar);
                TreeSet<Character> set = new TreeSet<>();
                for (char ss : s) set.add(ss);
                boolean flag = false;
                for (int i = K - 1; i >= 0; --i) {
                    set.remove(s[i]);
                    Character ss = set.higher(s[i]);
                    set.add(s[i]);

                    if (ss == null) continue;
                    t[i] = ss;

                    for (int j = i + 1; j < K; ++j) t[j] = set.first();
                    for (int j = 0; j < Math.min(i, n); ++j) t[j] = s[j];
                    flag = true;
                    break;
                }
                if (!flag) throw new RuntimeException();
            }
            out.println(new String(t));
        }

    }

    static class Debug {
        PrintWriter out;
        boolean oj;
        boolean system;
        long timeBegin;
        Runtime runtime;

        public Debug(PrintWriter out) {
            oj = System.getProperty("ONLINE_JUDGE") != null;
            this.out = out;
            this.timeBegin = System.currentTimeMillis();
            this.runtime = Runtime.getRuntime();
        }

        public Debug() {
            system = true;
            oj = System.getProperty("ONLINE_JUDGE") != null;
            OutputStream outputStream = System.out;
            this.out = new PrintWriter(outputStream);
            this.timeBegin = System.currentTimeMillis();
            this.runtime = Runtime.getRuntime();
        }

    }

    static class ArrayUtils {
        public static void fill(char[] array, char value) {
            Arrays.fill(array, value);
        }

    }

    static class FastReader {
        private InputStream stream;
        private byte[] buf = new byte[8192];
        private int curChar;
        private int pnumChars;

        public FastReader(InputStream stream) {
            this.stream = stream;
        }

        private int pread() {
            if (pnumChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= pnumChars) {
                curChar = 0;
                try {
                    pnumChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (pnumChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = pread();
            while (isSpaceChar(c))
                c = pread();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = pread();
            }
            int res = 0;
            do {
                if (c == ',') {
                    c = pread();
                }
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = pread();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public String nextString() {
            int c = pread();
            while (isSpaceChar(c))
                c = pread();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = pread();
            } while (!isSpaceChar(c));
            return res.toString();
        }

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

    }
}

