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.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Scanner;
import java.util.Set;
import java.util.Stack;
import java.util.TreeMap;

public class Main {
    static Scanner in;
    static int m;
    static String str;
    static char s[];
    static Set<Integer> ans = new HashSet<Integer>();

    public static void main(String[] args) throws FileNotFoundException {
        //        in = new Scanner(new File("input.txt"));
        in = new Scanner(System.in);
        m = in.nextInt();
        str = in.next();
        s = new char[str.length() + 1];
        for (int i = 1; i <= str.length(); i++) {
            s[i] = str.charAt(i - 1);
        }
        int i = 1;
        int l = s.length - 1;
        while (i <= l - m + 1) {
            int end = i + m - 1;
            if (end > l)
                end = l;
            int min = i;
            for (int j = i + 1; j <= end; j++) {
                if (s[j] <= s[min])
                    min = j;
            }
            ans.add(min);
            i = min + 1;
        }
        ArrayList<Character> result = new ArrayList<Character>();
        for (int j : ans) {
            result.add(s[j]);
        }
        Collections.sort(result);
        char worst = result.get(result.size() - 1);
        for (int j = 1; j <= l; j++) {
            if (s[j] < worst && !ans.contains(Integer.valueOf(j))) {
                ans.add(j);
                result.add(s[j]);
            }
        }
        Collections.sort(result);
        for (char c : result)
            System.out.print(c);
    }
}