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 javafx.util.Pair;

import java.util.Scanner;


public class Main{

    static boolean possible(char arr[], int m, char c){
        int length = 0;
        for(int i = 0; i < arr.length; i++){
            if(arr[i] <= c){
                length = 0;
            }else{
                length++;
                if(length == m){
                    return false;
                }
            }
        }
        return true;
    }

    static int solve(char arr[], int start, int end, char edge, int m){
        int length = 0;
        int lastInd = 0;
        int count = 0;
        for(int i = start; i < end; i++){
            length++;
            if(arr[i] == edge){
                lastInd = i;
            }
            if(length == m){
                count++;
                length = i - lastInd;
            }
        }
        return count;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int m = scanner.nextInt();
        String str = scanner.next();
        char[] arr = str.toCharArray();
        char edge = 'z';
        for(char i = 'a'; i <= 'z'; i++){
            if(possible(arr, m, i)){
                edge = i;
                break;
            }
        }

        int length = 0;
        int [] letters = new int[26];
        for(int i = 0; i < arr.length; i++){
            if(arr[i] < edge){
                letters[arr[i] - 'a']++;
                if(length >= m){
                    letters[edge - 'a'] += solve(arr, i - length, i, edge, m);
                }
                length = 0;
            }else{
                length++;
            }
        }

        if(length >= m){
            letters[edge - 'a'] += solve(arr, arr.length - length, arr.length, edge, m);
        }

        for(int i = 0; i < 26; i++){
            for(int j = 0; j < letters[i]; j++){
                System.out.print((char)(i + 'a'));
            }
        }
    }
}

