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".
#include <bits/stdc++.h>
using namespace std;
int m;
string s;
int cont[30];
int cont2[30];
int main() {
  scanf("%d", &m);
  cin >> s;
  char menor;
  for (int i = 0; i < m; i++) {
    cont[s[i] - 'a']++;
    cont2[s[i] - 'a']++;
    if (i == 0 || s[i] < menor) menor = s[i];
  }
  string menores = "";
  menores += menor;
  char maior = menor;
  for (int i = m; i < s.size(); i++) {
    cont[s[i] - 'a']++;
    cont2[s[i - m] - 'a']--;
    cont2[s[i] - 'a']++;
    if (s[i] < menor) {
      menor = s[i];
    } else if (cont2[menor - 'a'] == 0) {
      for (int j = 'a'; cont2[j - 'a'] == 0; j++) menor = j + 1;
    }
    menores += menor;
    if (menor > maior) maior = menor;
  }
  int vezes = 0;
  int ult = -1;
  for (int i = m - 1; i < s.size(); i++) {
    if (menores[i - m + 1] == maior) {
      while (s[i] != maior) i--;
      i += m - 1;
      vezes++;
    }
  }
  for (int i = 'a'; i < maior; i++) {
    for (int j = 0; j < cont[i - 'a']; j++) printf("%c", i);
  }
  for (int i = 0; i < vezes; i++) printf("%c", maior);
  printf("\n");
}
