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.PrintStream;
import java.util.stream.IntStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Wolfgang Beyer
 */
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 n = s.length();
            char[] c = new char[n];
            for (int i = 0; i < n; i++) {
                c[i] = s.charAt(i);
            }

            char current = 'a' - 1;
            boolean isValid = false;
            do {
                current++;
                //System.out.println("checking " + current);
                int lastValid = -1;
                isValid = true;
                for (int i = 0; i < n; i++) {
                    if (c[i] <= current) lastValid = i;
                    else if (i - lastValid >= m) {
                        //System.out.println(current + " not valid");
                        isValid = false;
                        break;
                    }
                }
            } while ((!isValid) && (current <= 'z'));
            //System.out.println(current + " is valid");

            int prev = -1;
            int next = -1;
            int essential = 0;
            for (int i = 0; i < n; i++) {
                if (c[i] < current) prev = i;
                if (c[i] == current) {
                    next = i + 1;
                    while ((next < n) && (c[next] >= current)) next++;
                    //if (next == n) next--;
                    //System.out.println("pos " + i + ": prev = " + prev + ", next = " + next);
                    if (next - prev > m) {
                        int nextCurrent = i + 1;
                        while ((nextCurrent < n) && (c[nextCurrent] != current)) nextCurrent++;
                        //if (nextCurrent == n) nextCurrent--;
                        if ((nextCurrent - prev > m)) {
                            //System.out.println("essential at " + i);
                            prev = i;
                            essential++;
                        }
                    }
                }
            }

            //System.out.println(essential);

            char x = 'a';
            StringBuilder sb = new StringBuilder();
            while (x < current) {
                int count = StringFunctions.countChar(s, x);
                //System.out.println(x + ": " + count);

                for (int i = 0; i < count; i++) {
                    sb.append(x);
                }
                x++;
            }
            for (int i = 0; i < essential; i++) {
                sb.append(current);
            }
            out.println(sb.toString());
        }

    }

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

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

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

        public String next() {
            try {
                while (tok == null || !tok.hasMoreTokens()) {
                    tok = new StringTokenizer(in.readLine());
                }
            } catch (IOException ex) {
                System.err.println("An IOException was caught :" + ex.getMessage());
            }
            return tok.nextToken();
        }

    }

    static class StringFunctions {
        public static int countChar(String s, char c) {
            return (int) s.chars().filter(ch -> ch == c).count();
        }

    }
}

