You are given a string s, consisting of lowercase English letters, and the integer m.

One should choose some symbols from the given string so that any contiguous subsegment of length m has at least one selected symbol. Note that here we choose positions of symbols, not the symbols themselves.

Then one uses the chosen symbols to form a new string. All symbols from the chosen position should be used, but we are allowed to rearrange them in any order.

Formally, we choose a subsequence of indices 1 ≤ i1 < i2 < ... < it ≤ |s|. The selected sequence must meet the following condition: for every j such that 1 ≤ j ≤ |s| - m + 1, there must be at least one selected index that belongs to the segment [j, j + m - 1], i.e. there should exist a k from 1 to t, such that j ≤ ik ≤ j + m - 1.

Then we take any permutation p of the selected indices and form a new string sip1sip2... sipt.

Find the lexicographically smallest string, that can be obtained using this procedure.

Input

The first line of the input contains a single integer m (1 ≤ m ≤ 100 000).

The second line contains the string s consisting of lowercase English letters. It is guaranteed that this string is non-empty and its length doesn't exceed 100 000. It is also guaranteed that the number m doesn't exceed the length of the string s.

Output

Print the single line containing the lexicographically smallest string, that can be obtained using the procedure described above.

Examples

Input

3
cbabc


Output

a


Input

2
abcab


Output

aab


Input

3
bcabcbaccba


Output

aaabb

Note

In the first sample, one can choose the subsequence {3} and form a string "a".

In the second sample, one can choose the subsequence {1, 2, 4} (symbols on this positions are 'a', 'b' and 'a') and rearrange the chosen symbols to form a string "aab".
import java.io.*;
import java.util.*;

import static java.lang.Math.*;

public class Main {
    FastScanner in;
    PrintWriter out;

    static final String FILE = "";

    int n, m;
    String s;

    StringBuffer buffer;
    TreeSet<Integer> filled;

    boolean isCover() {
        if (filled.isEmpty())
            return false;
        for (int i = 0; i < s.length(); i++) {
            if (i + m > s.length())
                break;
            int right = (filled.last() >= i) ? filled.higher(i - 1) : Integer.MAX_VALUE;
            if (abs(i - right) >= m)
                return false;
        }
        return true;
    }

    void solve() {
        m = in.nextInt();
        s = in.next();
        n = s.length();
        buffer = new StringBuffer();
        filled = new TreeSet<>();
        for (char c = 'a'; c <= 'z'; c++) {
            List<Integer> list = new ArrayList<>();
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == c)
                    list.add(i);
            }
            for (Integer it : list)
                filled.add(it);

            //if (filled.isEmpty())
            //    continue;

            if (isCover()) {
                int real = list.size();
                int mini = filled.first();
                for (Integer it : list) {
                    int pos = (mini == it) ? 0 : filled.lower(it) + 1;
                    int nval = (filled.last() > it) ? filled.higher(it) : Integer.MAX_VALUE;
                    int dist = abs(nval - pos);
                    if (dist < m || pos + m > s.length()) {
                        filled.remove(it);
                        mini = filled.first();
                        real--;
                    }
                }
                for (int i = 0; i < real; i++)
                    buffer.append(c);
                break;
            } else {
                for (int i = 0; i < list.size(); i++)
                    buffer.append(c);
            }
        }
        out.print(buffer.toString());
    }

    public void run() {
        if (FILE.equals("")) {
            in = new FastScanner(System.in);
            out = new PrintWriter(System.out);
        } else {
            try {
                in = new FastScanner(new FileInputStream(FILE +
                        ".in"));
                out = new PrintWriter(new FileOutputStream(FILE +
                        ".out"));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }
        solve();
        out.close();
    }

    public static void main(String[] args) {
        (new Main()).run();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner(InputStream is) {
            br = new BufferedReader(new InputStreamReader(is));
        }

        public String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        public String nextLine() {
            st = null;
            try {
                return br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
                return null;
            }
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }

        public float nextFloat() {
            return Float.parseFloat(next());
        }
    }

}