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.OutputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.io.BufferedWriter;
import java.util.Collection;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.util.Queue;
import java.io.BufferedReader;
import java.util.LinkedList;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author phantom11
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        TaskD solver = new TaskD();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskD {
        public void solve(int testNumber, InputReader in, OutputWriter out) {
            int i, j, m = in.nextInt();
            String s = in.next();
            Queue<Integer> queue[] = new Queue[26];
            for (i = 0; i < 26; i++) {
                queue[i] = new LinkedList<>();
            }
            int n = s.length();
            int counter[] = new int[26];
            for (i = 0; i < n; i++) {
                queue[s.charAt(i) - 'a'].add(i);
                counter[s.charAt(i) - 'a']++;
            }
            StringBuilder ans = new StringBuilder("");

            int used[] = new int[26];
            int last = -1;
            while (last == -1 || (last + m) < n) {
                int index = -1;
                for (j = 0; j < 26; j++) {
                    if (!queue[j].isEmpty() && (queue[j].peek() - last <= m)) {
                        index = j;
                        used[index]++;
                        break;
                    }
                }
                if (index >= 0) {
                    int temp = -1;
                    while (!queue[index].isEmpty() && (queue[index].peek() - last <= m)) {
                        temp = queue[index].poll();
                    }
                    last = temp;
                    for (j = 0; j < 26; j++) {
                        while (!queue[j].isEmpty() && (queue[j].peek()) <= last) {
                            queue[j].poll();
                        }
                    }
                }
            }
            int lastUsed = -1;
            for (i = 0; i < 26; i++) {
                if (used[i] > 0) {
                    lastUsed = i;
                }
            }
            for (i = 0; i < lastUsed; i++) {
                for (j = 0; j < counter[i]; j++) {
                    ans.append((char) (i + 'a'));
                }
            }
            for (i = 0; i < used[lastUsed]; i++) {
                ans.append((char) (lastUsed + 'a'));
            }
            char c[] = ans.toString().toCharArray();
            Arrays.sort(c);


            for (i = 0; i < c.length; i++) {
                out.print(c[i]);
            }
            out.printLine();
        }

    }

    static class InputReader {
        BufferedReader in;
        StringTokenizer tokenizer = null;

        public InputReader(InputStream inputStream) {
            in = new BufferedReader(new InputStreamReader(inputStream));
        }

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

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

    }

    static class OutputWriter {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream) {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer) {
            this.writer = new PrintWriter(writer);
        }

        public void print(Object... objects) {
            for (int i = 0; i < objects.length; i++) {
                if (i != 0)
                    writer.print(' ');
                writer.print(objects[i]);
            }
        }

        public void printLine(Object... objects) {
            print(objects);
            writer.println();
        }

        public void close() {
            writer.close();
        }

    }
}

