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 n;
vector<char> ans;
int b[100005], book[100005];
char ch[100005];
int check(int k) {
  memset(book, 0, sizeof(book));
  int len = strlen(ch);
  int flag = 1;
  for (int i = 0; i < len; i++) {
    if (ch[i] <= k)
      b[i] = 0;
    else
      b[i] = b[i - 1] + 1;
    if (b[i] >= n) flag = 0;
  }
  return flag;
}
int main() {
  scanf("%d", &n);
  scanf(" %s", ch);
  int len = strlen(ch);
  for (int i = 'a'; i <= 'z'; i++) {
    if (check(i)) {
      int first = -1, last = -1;
      for (int j = 0; j < len; j++) {
        if (ch[j] < i) {
          book[j]++;
          first = -1;
          last = -1;
        } else {
          if (first == -1) first = j;
          if (ch[j] == i) last = j;
          if (first != -1 && j - first == n - 1) {
            book[last] = 1;
            j = last;
            first = -1;
            last = -1;
          }
        }
      }
      for (int j = 0; j < len; j++) {
        if (book[j] || ch[j] < i) ans.push_back(ch[j]);
      }
      break;
    }
  }
  sort(ans.begin(), ans.end());
  for (int i = 0; i < ans.size(); i++) printf("%c", ans[i]);
  return 0;
}
