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.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class DenseSubsequence {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		char[] word = scan.next().toCharArray();
		outer: for(char c = 'a'; c <= 'z'; c++){
			int last = -1, count = 1, index = 0;		
			ArrayList<Character> out = new ArrayList<Character>();
			while(true){
				if(count > n){
					if(last == -1) continue outer;
					count = 1;
					index = last+1;
					last = -1;
					out.add(c);
				}
				if(index >= word.length) break;
				if(word[index] < c){
					out.add(word[index]);
					count = 0;
					last = -1;
				}
				if(word[index] == c) last = index;
				count++;
				index++;
			}
			Collections.sort(out);
			for(char o : out)System.out.print(o);
			break;
		}
	}
}
