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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.BufferedReader;
import java.util.regex.Pattern;
import java.io.InputStreamReader;
import java.io.InputStream;

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

    static class TaskD {
        boolean[] busy;
        String s;
        int n;
        int m;

        int calc(final char c) {
            int count = 0;
            int l = -1;
            int p = -1;
            boolean useAll = false;
            for (int r = 0; r < n; r++) {
                if (busy[r]) {
                    l = r;
                } else if (s.charAt(r) == c) {
                    p = r;
                }

                if (r - l + 1 > m) {
                    if (p > l) {
                        count++;
                        busy[p] = true;
                        l = p;
                    } else {
                        useAll = true;
                        break;
                    }
                }
            }
            if (useAll) {
                count = 0;
                for (int i = 0; i < n; i++) {
                    if (s.charAt(i) == c) {
                        busy[i] = true;
                        count++;
                    }
                }
            }

            return count;
        }

        public void solve(int testNumber, FastScanner in, PrintWriter out) {
            m = in.nextInt();
            s = in.nextLine();
            n = s.length();
            busy = new boolean[n];

            for (char c = 'a'; c <= 'z'; c++) {
                int count = calc(c);
                if (count == 0 && s.indexOf(c) >= 0) break;
                for (int i = 0; i < count; i++) {
                    out.print(c);
                }
            }

        }

    }

    static class FastScanner {
        final BufferedReader input;
        String[] buffer;
        int pos;
        final static Pattern SEPARATOR = Pattern.compile("\\s+");

        public FastScanner(InputStream inputStream) {
            input = new BufferedReader(new InputStreamReader(inputStream));
        }

        private String read() {
            try {
                if (buffer == null || pos >= buffer.length) {
                    buffer = SEPARATOR.split(input.readLine());
                    pos = 0;
                }
                return buffer[pos++];
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }
        }

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

        public String nextLine() {
            if (buffer != null && pos < buffer.length) {
                throw new RuntimeException("Buffer is not empty");
            }
            try {
                return input.readLine();
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }
        }

    }
}

