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.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.StringTokenizer;


public class D {
	public static void main(String[] args) {
		InputReader in = new InputReader(System.in);
        PrintWriter out = new PrintWriter(System.out);
        int m = in.nextInt();
        String str = in.next();
        char[] chs = str.toCharArray();
        P[][] max = new P[chs.length][20];
        int n = (int)Math.floor(Math.log((double)chs.length)/Math.log(2.0));
        for(int i=0;i<chs.length;i++){
        	max[i][0] = new P(chs[i],i);
        }
        for(int i=1;i<=n;i++){
        	for(int j=0;j<chs.length;j++){
        		int t = j+(1<<(i-1));
    			max[j][i] = max[j][i-1];
        		if(t<chs.length && max[t][i-1].c<=max[j][i].c){
        			max[j][i] = max[t][i-1];
        		}
        	}
        }
        char maxC='a';
        for(int i=0;i+m-1<chs.length;i++){
        	P mm = rmq(max, i, i+m-1);
        	if(mm.c>maxC) maxC = mm.c;
        }
//        System.out.println(maxC);
        boolean[] cvd = new boolean[chs.length];
        boolean[] cr = new boolean[chs.length];
        for(int i=0;i<cvd.length;i++) {
        	cvd[i] = false;
        	cr[i] = false;
        }
        
        ArrayList<Character> res = new ArrayList<>();
        int prev = -1;
        for(int i=0;i<chs.length;i++){
        	if(chs[i]<maxC){
        		res.add(chs[i]);
        		cvd[i] = true;
        	}

        }
        
        for(int i=0;i+m-1<chs.length;i++){
        	if(cr[i]) continue;
        	P mm = rmq(max, i, i+m-1);
        	if(!cvd[mm.index]){
        		res.add(chs[mm.index]);
        		cvd[mm.index] = true;
        		for(int j=i+1;j<=mm.index;j++){
        			cr[j] = true;
        		}
        	}
        }
        res.sort(null);
        for(int i=0;i<res.size();i++){
        	out.print(res.get(i));
        }
        out.println();
        out.flush();
	}
	
	static P rmq(P[][] max, int i, int j){
    	int n = (int)Math.floor(Math.log((double)j-i+1)/Math.log(2.0));
    	P mm = max[i][n];
    	if(max[j-(1<<n)+1][n].c <= mm.c) mm = max[j-(1<<n)+1][n];
    	return mm;
	}
	static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }
        
        public long nextLong(){
        	return Long.parseLong(next());
        }

    }
}

class P{
	char c;
	int index;
	
	P(char c, int index){
		this.c = c;
		this.index = index;
	}
}