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

public class D {
    FastScanner in;
    PrintWriter out;

    int[] ans = new int[26];
    char[] s;
    int m;
    void get(int l, int r) {
        char min = getMin(l, r);
        List<Integer> list = getList(l, r, min);
        boolean ok = isOk(list);
        if (ok) {
            int last = l - 1;
            for (int i = 1; i < list.size() - 1; i++) {
                if (list.get(i + 1) - last - 1 >= m) {
                    ans[s[list.get(i)] - 'a']++;
                    last = list.get(i);
                }
            }
        } else {
            ans[s[list.get(1)] - 'a'] += list.size() - 2;
            for (int i = 0; i < list.size() - 1; i++) {
                if (list.get(i + 1) - list.get(i) - 1 >= m) {
                    get(list.get(i) + 1, list.get(i + 1));
                }
            }
        }
    }

    private boolean isOk(List<Integer> list) {
        for (int i = 0; i < list.size() - 1; i++) {
            if (list.get(i + 1) - list.get(i) - 1 >= m) {
                return false;
            }
        }
        return true;
    }

    private List<Integer> getList(int l, int r, char min) {
        List<Integer> list = new ArrayList<>();
        list.add(l - 1);
        for (int i = l; i < r; i++) {
            if (s[i] == min) {
                list.add(i);
            }
        }
        list.add(r);
        return list;
    }

    private char getMin(int l, int r) {
        char min = (char)('z' + 1);
        for (int i = l; i < r; i++) {
            if (min > s[i]) {
                min = s[i];
            }
        }
        return min;
    }

    public void solve() throws IOException {
        m = in.nextInt();
        s = in.next().toCharArray();
        get(0, s.length);

        int index = 25;
        while (ans[index] == 0) {
            index--;
        }
        char c = (char) (index + 'a');
        List<Character> list = new ArrayList<>();
        for (int i = 0; i < s.length; i++) {
            if (s[i] < c) {
                list.add(s[i]);
            }
        }
        for (int i = 0; i < ans[index]; i++) {
            list.add(c);
        }
        Collections.sort(list);
        StringBuilder sb = new StringBuilder();
        for (char cc : list) {
            sb.append(cc);
        }
        out.println(sb);
    }

    public void run() {
        try {
            in = new FastScanner(System.in);
            out = new PrintWriter(System.out);
            Locale.setDefault(Locale.US);

            solve();

            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;

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

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

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

    public static void main(String[] arg) {
        new D().run();
    }
}