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.*;
import java.util.*;

public class B {

	static final int INF = (int)1e9;
	public static void main(String[] args) throws IOException {

		Scanner sc = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);

		int m = sc.nextInt();
		char[] s = sc.next().toCharArray();
		int n = s.length;
		
		boolean[] taken = new boolean[n];
		for(int j = 0; j < 26; ++j)
		{
			boolean good = true;
			int lstChar = -1, lstUncovered = 0;
			for(int i = 0; i < n; ++i)
			{
				if(s[i] - 'a' == j)
					lstChar = i;
				else if(s[i] - 'a' < j)
				{
					lstUncovered = i + 1;
					lstChar = -1;
					taken[i] = true;
				}
				if(i - lstUncovered + 1 < m)
					continue;
				if(lstChar == -1)
					good = false;
				else
				{
					taken[lstChar] = true;
					lstUncovered = lstChar + 1;
					lstChar = -1;
				}
			}
			if(good)
				break;
		}
		StringBuilder sb = new StringBuilder();
		for(int i = 0; i < n; ++i)
			if(taken[i])
				sb.append(s[i]);
		Arrays.sort(s = sb.toString().toCharArray());
		out.println(s);
		out.close();
	}
	static class Scanner
	{
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s){	br = new BufferedReader(new InputStreamReader(s));}

		public Scanner(FileReader s) throws FileNotFoundException {	br = new BufferedReader(s);}

		public String next() throws IOException
		{
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

		public int nextInt() throws IOException {return Integer.parseInt(next());}

		public long nextLong() throws IOException {return Long.parseLong(next());}

		public String nextLine() throws IOException {return br.readLine();}

		public double nextDouble() throws IOException { return Double.parseDouble(next()); }

		public boolean ready() throws IOException {return br.ready();}
	}
}