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.util.*;
import java.io.*;
public class Main {
public static void main(String [] args)throws Exception{
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	int m = Integer.parseInt(br.readLine());
	String str = br.readLine();
	TreeSet<Integer>set = new TreeSet<Integer>();
	ArrayList<Integer>pos[] = new ArrayList[26];
	for(int i = 0;i < pos.length;i++)
		pos[i] = new ArrayList<Integer>();
	for(int i = 0;i < str.length();i++){
		pos[str.charAt(i) - 'a'].add(i);
	}
	int array[] = new int[26];
	int last = 0;
	for(int i = 0;i < 26;i++){
		for(int temp : pos[i])
			set.add(temp);
		boolean flag = true;
		for(int j = 0;j < str.length() - m + 1;j++){
			Integer val = set.floor(j + m - 1);
			if(val == null || val < j){
				flag = false;
				break;
			}
		}
		if(flag){
            last = i;
			break;
		}
		array[i] = pos[i].size();
	}
	TreeSet<Integer>diffset = new TreeSet<Integer>();
	for(int temp : pos[last]){
			set.remove(temp);
			diffset.add(temp);
	}
	int current = 0;
	//System.out.println(last);
	while(current < str.length() - m + 1){
		Integer val = set.floor(current + m - 1);
		if(val == null || val < current){
		val = diffset.floor(current + m - 1);
		current = val;
		array[last]++;
	}
	++current;
	}
	StringBuilder sb = new StringBuilder();
	for(int i = 0;i < array.length;i++){
		for(int j = 1;j <= array[i];j++)
			sb.append((char)(97 + i));
	}
	System.out.println(sb);
}
}