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>
inline int F() {
  register int aa, bb, ch;
  while (ch = getchar(), (ch < '0' || ch > '9') && ch != '-')
    ;
  ch == '-' ? aa = bb = 0 : (aa = ch - '0', bb = 1);
  while (ch = getchar(), ch >= '0' && ch <= '9') aa = aa * 10 + ch - '0';
  return bb ? aa : -aa;
}
const int Maxn = 100010;
int cnt[26];
char s[Maxn];
int main() {
  int m = F(), flag = 0;
  scanf("%s", s + 1);
  int n = strlen(s + 1);
  for (int i = 0; i <= n; ++i) {
    int lst = 0;
    for (int j = 1; j <= n; ++j) {
      if (j - lst > m) {
        goto End;
      }
      if (s[j] - 'a' <= i) lst = j;
    }
    flag = i;
    break;
  End:
    1;
  }
  int lst = 0, lsti = 0;
  for (int i = 1; i <= n; ++i) {
    if (i - lst > m) {
      ++cnt[flag];
      lst = lsti;
    }
    if (s[i] - 'a' == flag) lsti = i;
    if (s[i] - 'a' < flag) ++cnt[s[i] - 'a'], lst = i;
  }
  if (!flag && !cnt[0])
    puts("a");
  else
    for (int i = 0; i <= flag; ++i)
      while (cnt[i]--) printf("%c", i + 'a');
}
