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".
// package CF;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.SortedSet;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.function.Consumer;


public class A {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		int m = sc.nextInt();
		char [] s = sc.next().toCharArray();
		TreeSet<Integer> ch [] = new TreeSet[26];
		for (int i = 0; i < ch.length; i++) {
			ch[i] = new TreeSet<>();
		}
		TreeSet<Integer> inter = new TreeSet<>();
		for (int i = 0; i < s.length; i++) {
			ch[s[i]-'a'].add(i);
			if(i+m-1 < s.length)
				inter.add(i+m-1);
		}
		StringBuilder sb = new StringBuilder();
		for (char c = 'a'; c <= 'z'; c++) {
			TreeSet<Integer> ts = new TreeSet<Integer>(inter);
//			System.out.println(ch[c-'a']);
			int max = -1;
			for(Iterator<Integer> it = ts.iterator(); it.hasNext();){
				int i = it.next();
				if(i <= max)
					continue;
				Integer tmp = ch[c-'a'].floor(i);
				if(tmp == null || i-tmp+1 > m)
					break;
				max = Math.max(max, tmp+m-1);
				SortedSet<Integer> tt = new TreeSet<Integer>(inter.subSet(tmp, tmp+m));
				inter.removeAll(tt);
				sb.append(c);
				ch[c-'a'].remove(tmp);
			}
			if(inter.size() == 0)
				break;
			for(int i:ch[c-'a']){
				sb.append(c);
				SortedSet<Integer> tt = new TreeSet<Integer>(inter.subSet(i, i+m));
				inter.removeAll(tt);		
			}
		}
		out.println(sb);
		out.flush();
		out.close();
	}
	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

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

		public Scanner(FileReader fileReader) {
			br = new BufferedReader(fileReader);
		}

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