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.InputMismatchException;
import java.io.IOException;
import java.util.TreeSet;
import java.util.ArrayList;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.util.Collections;
import java.io.InputStream;
/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Alex
 */
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 {
        int m;
        int[] s;
        ArrayList<Integer> res = new ArrayList<>();
        int TWENTY_SIX = 26;
        TreeSet<Integer> added = new TreeSet<>();
        TreeSet<Integer> bad = new TreeSet<>();
        void fix(int idx) {
            if (!added.isEmpty()) {
                Integer closest = added.floor(idx);
                if (closest != null) {
                    if (idx - closest < m) return;
                }
            }
            Integer best = bad.floor(idx);
            added.add(best);
        }
        public void solve(int testNumber, InputReader in, OutputWriter out) {
            m = in.readInt();
            char[] ss = in.next().toCharArray();
            int n = ss.length;
            s = new int[n];
            for (int i = 0; i < s.length; i++) s[i] = (int) (ss[i] - 'a');
            int WORST = 0;
            int[] count = new int[TWENTY_SIX];
            for (int i = 0; i < n; i++) {
                count[s[i]]++;
                if (i >= m) count[s[i - m]]--;
                if (i >= m - 1) {
                    for (int j = 0; j < TWENTY_SIX; j++) {
                        if (count[j] > 0) {
                            WORST = Math.max(WORST, j);
                            break;
                        }
                    }
                }
            }
            for (int a : s) if (a < WORST) res.add(a);
            Collections.sort(res);
            for (int i = 0; i < s.length; i++) if (s[i] == WORST) bad.add(i);
            Arrays.fill(count, 0);
            for (int i = 0; i < n; i++) {
                count[s[i]]++;
                if (i >= m) count[s[i - m]]--;
                if (i >= m - 1) {
                    for (int j = 0; j < TWENTY_SIX; j++) {
                        if (count[j] > 0) {
                            if (j == WORST) {
                                fix(i);
                            }
                            break;
                        }
                    }
                }
            }
            for (int i = 0; i < added.size(); i++) res.add(WORST);
            for (int val : res) out.print((char) (val + 'a'));
            out.printLine();
        }
    }
    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 printLine() {
            writer.println();
        }
        public void print(char i) {
            writer.print(i);
        }
        public void close() {
            writer.close();
        }
    }
    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private InputReader.SpaceCharFilter filter;
        public InputReader(InputStream stream) {
            this.stream = stream;
        }
        public int read() {
            if (numChars == -1)
                throw new InputMismatchException();
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }
        public int readInt() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }
        public String readString() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                if (Character.isValidCodePoint(c))
                    res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }
        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return isWhitespace(c);
        }
        public static boolean isWhitespace(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
        public String next() {
            return readString();
        }
        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }
}

