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;
char str[100005];
int cnt[26];
int ask[100005];
int quq[100005];
set<int> vec;
set<int>::iterator it;
int main(void) {
  int n;
  int i, j;
  while (scanf("%d", &n) != EOF) {
    vec.clear();
    scanf("%s", str + 1);
    int l = strlen(str + 1);
    memset(cnt, 0, sizeof(cnt));
    for (i = 1; i <= l; i++) {
      cnt[str[i] - 'a']++;
    }
    int head = 1;
    int rail = 0;
    int cn = 0;
    for (i = 1; i <= n; i++) {
      if (head > rail) {
        quq[++rail] = i;
      } else {
        while (true) {
          if (head > rail) break;
          int id = quq[rail];
          if (str[id] >= str[i]) {
            rail--;
          } else
            break;
        }
        quq[++rail] = i;
      }
    }
    vec.insert(quq[head]);
    for (i = n + 1; i <= l; i++) {
      while (true) {
        if (head > rail) break;
        int id = quq[rail];
        if (str[id] >= str[i] && !vec.count(id)) {
          rail--;
        } else
          break;
      }
      quq[++rail] = i;
      int ic = quq[head];
      while (ic < i - n + 1) {
        head++;
        ic = quq[head];
      }
      vec.insert(quq[head]);
    }
    for (it = vec.begin(); it != vec.end(); it++) {
      ask[cn++] = str[*it] - 'a';
      cnt[ask[cn - 1]]--;
    }
    sort(ask, ask + cn);
    int maxx = ask[cn - 1];
    for (i = 0; i < 26; i++) {
      if (i < maxx) {
        while (cnt[i]) {
          ask[cn++] = i;
          cnt[i]--;
        }
      }
    }
    sort(ask, ask + cn);
    for (i = 0; i < cn; i++) printf("%c", ask[i] + 'a');
    printf("\n");
  }
  return 0;
}
