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;
char str[100010];
char _str[100010];
int _cnt[26];
int len;
bool cnt;
bool C(int k) {
  int cnt = 1;
  for (int i = 0; i < len; i++) {
    if (str[i] - 'a' < k)
      cnt = 1;
    else
      cnt++;
    if (cnt > m) return false;
  }
  return true;
}
int solve(int k) {
  int res = 0;
  int cnt = 1, last = -1;
  for (int i = 0; i < len; i++) {
    if (str[i] - 'a' < k)
      cnt = 1;
    else
      cnt++;
    if (str[i] - 'a' == k) last = i;
    if (cnt > m) {
      cnt = i - last;
      res++;
      cnt = max(1, cnt);
    }
  }
  return res;
}
int main() {
  scanf("%d", &m);
  scanf("%s", str);
  len = strlen(str);
  for (int i = 0; i < len; i++) {
    _cnt[str[i] - 'a']++;
  }
  int l = 0, r = 26;
  while (r - l > 1) {
    int m = (l + r) / 2;
    if (C(m))
      r = m;
    else
      l = m;
  }
  int ans = solve(l);
  if (m >= len) {
    for (int i = 0; i < 26; i++)
      if (_cnt[i] > 0) {
        printf("%c", i + 'a');
        break;
      }
  } else {
    _cnt[l] = ans;
    for (int i = 0; i <= l; i++) {
      while (_cnt[i] > 0) {
        _cnt[i]--;
        printf("%c", i + 'a');
      }
    }
  }
  printf("\n");
}
