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 {
        int m;
        String a;
        int cnt[] = new int[27];

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            m = in.nextInt();
            a = in.next();

            for (int i = 0; i < a.length(); i++) {
                cnt[a.charAt(i) - 'a']++;
            }

            for (char ch = 'a'; ch <= 'z'; ch++) {
                if (m == a.length()) {
                    if (cnt[ch - 'a'] > 0) {
                        out.print(ch);
                        break;
                    }
                    continue;
                }

                int req = isAdequate(ch);
                for (int i = 0; i < Math.min(req, cnt[ch - 'a']); i++)
                    out.print(ch);
                if (req < Integer.MAX_VALUE)
                    break;
            }
            out.flush();
        }

        public int isAdequate(char ch) {
            int last = -1, lastL = -1, req = 0;
            for (int i = 0; i < a.length(); i++) {
                if (a.charAt(i) < ch) lastL = i;
                if (a.charAt(i) == ch) last = i;
                if (i - lastL >= m) {
                    if (last > lastL) {
                        req++;
                        lastL = last;
                    } else
                        return Integer.MAX_VALUE;
                }
            }
            return req;
        }

    }

    static class InputReader {
        private BufferedReader in;
        private StringTokenizer st;

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

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

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

    }
}

