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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class Test1 {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int m = scanner.nextInt();
        scanner.nextLine();
        String s = scanner.nextLine();

        int lastSelected = -1;
        int[] chars = new int[30];
        for (int i = 0; i < s.length(); i++) {
            chars[s.charAt(i) - 'a']++;
        }

        int maxCh = -1;
        int maxChCount = 0;
        for (int i = 0; i < s.length() - m + 1; i++) {
            int end = i + m - 1;
            if (lastSelected >= i && lastSelected <= end) {
                continue;
            }
            int minIndex = -1;
            char minCh = ' ';
            for (int j = end; j >= i; j--) {
                char ch = s.charAt(j);
                if (minCh == ' ' || ch < minCh) {
                    minCh = ch;
                    minIndex = j;
                }
            }
            lastSelected = minIndex;

            int curCh = minCh - 'a';
            if (maxCh < curCh) {
                maxCh = curCh;
                maxChCount = 1;
            } else if (curCh == maxCh) {
                maxChCount++;
            }
        }
        StringBuilder builder = new StringBuilder();
        for (int j = 0; j < maxCh; j++) {
            for (int k = 0; k < chars[j]; k++) {
                builder.append((char) ('a' + j));
            }
        }
        for (int k = 0; k < maxChCount; k++) {
            builder.append((char) ('a' + maxCh));
        }
        System.out.println(builder.toString());
    }


    public static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String nextToken() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(nextToken());
        }

        long nextLong() {
            return Long.parseLong(nextToken());
        }

        double nextDouble() {
            return Double.parseDouble(nextToken());
        }
    }
}
