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.*;

public class Solve3 {

  public static void main(String[] args) {
	MyScanner scanner = new MyScanner();
	PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out));
    int m = scanner.nextInt();  
    String s = scanner.nextLine();
	
    StringBuilder sb = new StringBuilder();
	for(int c = 0; c <= 'z'-'a'; c++) {
	  char start = (char)('a'+c);
	  int prev = -1;
	  int prevc = -1;
	  boolean ok = true;
	  sb = new StringBuilder();
	  for(int i = 0; i < s.length(); i++) {
	    char cc = s.charAt(i);
		//System.out.println(start + " " + cc + " " + prevc + " " + prev + " ");
		if(cc < start) {
		  sb.append(cc);
		  prev = i;
		} else {
		  if(cc == start)
			prevc = i;
		  
          if(i-prev + 1 > m || (i == s.length()-1 && prev == -1)) {
		    if(prevc==-1 || i-prevc+1>m) {
			  ok = false;
			  break;
			} else {
			  sb.append(start);
			  prev = prevc;
			}
		  }
		}
	  }	
	  if(ok) break;
	}
	String res = sb.toString();
    char[] chars = res.toCharArray();
    Arrays.sort(chars);
    String newWord = new String(chars);


    out.println(newWord);
	out.close();
  }

  public 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());
      }
 
      String nextLine(){
          String str = "";
	  try {
	     str = br.readLine();
	  } catch (IOException e) {
	     e.printStackTrace();
	  }
	  return str;
      }

   }
}