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 ch[100002];
int main() {
  ios_base::sync_with_stdio(0);
  int i, j, x, n, cnt = 0, m, y, k, g, flg, p;
  string s, cs, an;
  cin >> m >> s;
  char mc = 'A';
  for (i = 0; i <= s.size() - m; i++) {
    char c = '|';
    p = i;
    for (j = i; j <= i + m - 1; j++) {
      if (s[j] < c) {
        c = s[j];
        p = j;
      } else if (s[j] == c) {
        p = j;
      }
    }
    an += c;
    mc = max(c, mc);
    i = p;
    ch[p] = 1;
  }
  for (i = 0; i <= s.size() - 1; i++) {
    if (!ch[i] && s[i] < mc) an += s[i];
  }
  sort(an.begin(), an.end());
  cout << an;
}
