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>
int dense(char c, char *cc, int l, int m) {
  int i, i_;
  i_ = -1;
  for (i = 0; i <= l; i++)
    if (i == l || cc[i] <= c) {
      if (i - i_ > m) return 0;
      i_ = i;
    }
  return 1;
}
int main() {
  char c;
  int i, m, l;
  static char cc[100000];
  static int ii[100000 + 2];
  static int jj[100000];
  scanf("%d", &m);
  scanf("%s", cc);
  l = strlen(cc);
  for (c = 'a'; c <= 'z'; c++) {
    if (dense(c, cc, l, m)) {
      int j, k1, k2;
      k1 = k2 = 0;
      ii[k1++] = -1;
      for (i = 0; i < l; i++)
        if (cc[i] < c) ii[k1++] = i;
      ii[k1++] = l;
      for (i = 0; i < l; i++)
        if (cc[i] == c) jj[k2++] = i;
      j = 0;
      for (i = 0; i < k2; i++) {
        while (j + 2 < k1 && ii[j + 1] < jj[i]) j++;
        if (ii[j + 1] - ii[j] > m && (i + 1 == k2 || jj[i + 1] - ii[j] > m)) {
          printf("%c", cc[jj[i]]);
          ii[j] = jj[i];
        }
      }
      printf("\n");
      return 0;
    } else
      for (i = 0; i < l; i++)
        if (cc[i] == c) printf("%c", cc[i]);
  }
  return 0;
}
