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.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.StringTokenizer;

public class DIntel {
	public static void main(String[] args) {
		MyScanner scan = new MyScanner();
		int M = scan.nextInt();
		String s = scan.next();
		int N = s.length();
		boolean[] take = new boolean[N];
		char max = 'a';
		for(int i=0;i<=N-M;i++){
			int min = 'z', minIdx = -1;
			for(int j=i;j<i+M;j++){
				if(s.charAt(j)<=min){
					min = s.charAt(j);
					minIdx = j;
				}
			}
			take[minIdx] = true;
			max = (char)Math.max((int)max, (int)min);
			i = minIdx;
		}
		ArrayList<Character> list = new ArrayList<>();
		for(int i=0;i<N;i++){
			if(take[i])list.add(s.charAt(i));
			else if (s.charAt(i)<max)list.add(s.charAt(i));
		}
		Collections.sort(list);
		StringBuilder sol = new StringBuilder("");
		for(char c : list)sol.append(c);
		PrintWriter out = new PrintWriter(System.out);
		out.println(sol);
		out.close();
	}
	private static class MyScanner {
		BufferedReader br;
		StringTokenizer st;
		public MyScanner()  {
			br = new BufferedReader(new InputStreamReader(System.in));
		}
		String next(){
			while(st==null||!st.hasMoreElements()){
				try{st = new StringTokenizer(br.readLine());}
				catch(IOException e){e.printStackTrace();}
			}return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong(){return Long.parseLong(next());}
		double nextDouble(){return Double.parseDouble(next());}
	}
}
