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.*;
import java.math.*;
import static java.lang.Math.*;
import static java.lang.Integer.parseInt;
import static java.lang.Long.parseLong;
import static java.lang.Double.parseDouble;
import static java.lang.String.*;

public class Main {
    
    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        StringBuilder out = new StringBuilder();
        StringTokenizer tk;
        
        int m = parseInt(in.readLine());
        char [] g = in.readLine().toCharArray();
        boolean [] a = new boolean[g.length];
        
        for(char c='a'; c<='z'; c++) {
            int last = -1,rang = -1;
            
            for(int i=0; i<g.length; i++) {
                if(g[i]<c && a[i]) {
                    if(i-rang > m && last!=-1) {
                        out.append(c);
                        a[last] = true;
                        //System.out.println(last+" *");
                        last = -1;
                    } else if(i-rang <= m) last = -1;
                    rang = i;
                }
                
                if(g[i]==c) {
                    if(i-rang <= m) {
                        last = i;
                    } else {
                        if(last==-1) {
                            //if(!a[i]) {
                                out.append(c);
                                a[i] = true;
                               // System.out.println(i+" *");
                                rang = i;
                            //} else last = i;
                        } else {
                            out.append(c);
                            a[last] = true;
                            //System.out.println(last+" *");
                            rang = last;
                            last = i;
                        }
                    }
                }
            }
            
            if(last!=-1 && g.length-rang > m) {
                out.append(c);
                a[last] = true;
               // System.out.println(last+" *");
            }
            //System.out.println("***********");
            
            boolean f = true;
            rang = -1;
            for(int i=0; i<g.length; i++) {
                if(a[i] && i-rang > m) {
                    f = false;
                    rang = i;
                    break;
                } else if(a[i]) {
                    rang = i;
                }
            }
            if(g.length-rang > m) {
                for(int i=0; i<g.length; i++) {
                    if(g[i]==c && !a[i]) {
                        a[i] = true;
                        out.append(c);
                    }
                }
                f = false;
            }
            
            if(f) {
                System.out.println(out);
                return;
            }
        }
        
    }
}
