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.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

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

    static class TaskD {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int m = in.nextInt();
            String s = in.next();
            int[] cnt = new int[26];
            for (int i = 0; i < s.length(); i++) {
                cnt[s.charAt(i) - 'a']++;
            }
            char biggerChar = 'a';
            boolean[] used = new boolean[s.length()];
            loop:
            for (; biggerChar <= 'z'; biggerChar++) {
                for (int i = 0; i < s.length(); i++) {
                    if (s.charAt(i) == biggerChar) {
                        used[i] = true;
                    }
                }
                int gap = 0;
                for (int i = 0; i < s.length(); i++) {
                    if (used[i]) {
                        gap = 0;
                    } else {
                        gap++;
                    }
                    if (gap == m) continue loop;
                }
                break;
            }
            used = new boolean[s.length()];
            for (char c = 'a'; c < biggerChar; c++) {
                for (int i = 0; i < s.length(); i++) {
                    if (s.charAt(i) == c) {
                        used[i] = true;
                    }
                }
            }
            int gap = 0, last = 0, biggerCharCnt = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == biggerChar) {
                    last = i;
                }
                if (used[i]) {
                    gap = 0;
                } else {
                    gap++;
                }
                if (gap == m) {
                    used[last] = true;
                    gap = i - last;
                    biggerCharCnt++;
                }
            }
            for (char c = 'a'; c < biggerChar; c++) {
                for (int i = 0; i < cnt[c - 'a']; i++) {
                    out.print(c);
                }
            }
            for (int i = 0; i < biggerCharCnt; i++) {
                out.print(biggerChar);
            }
        }

    }

    static class InputReader {
        private BufferedReader reader;
        private StringTokenizer stt;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream));
        }

        public String nextLine() {
            try {
                return reader.readLine();
            } catch (IOException e) {
                return null;
            }
        }

        public String next() {
            while (stt == null || !stt.hasMoreTokens()) {
                stt = new StringTokenizer(nextLine());
            }
            return stt.nextToken();
        }

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

    }
}

