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.*;
import java.util.*;

public class Cf724D {

    static char[] s;
    static char max = 'a';
    static boolean vis[];

    public static void main(String args[]) throws IOException {
        InputReader in = new InputReader(System.in);
        PrintWriter w = new PrintWriter(System.out);
        int win = in.nextInt();
        s = in.readString().toCharArray();
        int n = s.length;
        vis = new boolean[n];
        for (int i = 0; i < (n - win + 1); i++) {
            int p = solve(win, i);
            i = p;
        }
        
        StringBuilder answer = new StringBuilder();
        for (int i = 0; i < n; i++) {
            if (vis[i]) {
                answer.append(s[i]);
            } else if (s[i] < max) {
                answer.append(s[i]);
            }
        }
        char ans[] = answer.toString().toCharArray();
        Arrays.sort(ans);
        w.println(ans);
        w.close();
    }

    public static int solve(int win, int i) {
        if (i == 0) {
            char minimum = 'z';
            int p = 0;
            for (i = 0; i < win; i++) {
                if (minimum >= s[i]) {
                    minimum = s[i];
                    p = i;
                }
            }

            if (minimum > max) {
                max = minimum;
            }
            vis[p] = true;
            return p;
        } else {
            int p = i;
            char minimum = 'z';
            for (int j = i; j < (i+win); j++) {
                if (minimum >= s[j]) {
                    minimum = s[j];
                    p = j;
                }
            }
            
            if (minimum > max) {
                max = minimum;
            }
            //System.out.println(max);
            vis[p] = true;
            return p;
        }
    }

    static class InputReader {

        private InputStream stream;
        private byte[] buf = new byte[8192];
        private int curChar, snumChars;
        private SpaceCharFilter filter;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int snext() {
            if (snumChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= snumChars) {
                curChar = 0;
                try {
                    snumChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (snumChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = snext();
            while (isSpaceChar(c)) {
                c = snext();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = snext();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public long nextLong() {
            int c = snext();
            while (isSpaceChar(c)) {
                c = snext();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = snext();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public int[] nextIntArray(int n) {
            int a[] = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = nextInt();
            }
            return a;
        }

        public String readString() {
            int c = snext();
            while (isSpaceChar(c)) {
                c = snext();
            }
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = snext();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public interface SpaceCharFilter {

            public boolean isSpaceChar(int ch);
        }
    }
}
