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, n, cnt;
char s[100010], ans[100010], max_char;
bool ch[100010];
int main() {
  scanf("%d\n", &m);
  gets(s + 1);
  n = strlen(s + 1);
  int lp = 0;
  for (; lp <= n - m;) {
    int min_id = 'z' + 1, pos = 0;
    for (int i = lp + 1; i <= lp + m; i++)
      if (min_id >= s[i]) min_id = s[pos = i];
    ans[++cnt] = (char)min_id;
    ch[lp = pos] = true;
    max_char = max(max_char, (char)min_id);
  }
  for (int i = 1; i <= n; i++)
    if (!ch[i] && max_char > s[i]) ans[++cnt] = s[i];
  sort(ans + 1, ans + cnt + 1);
  for (int i = 1; i <= cnt; i++) printf("%c", ans[i]);
  printf("\n");
  return 0;
}
