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;
bool check(string& s, char c, int cnt, int m) {
  int last_seen_c = -1 - m;
  int cur_cov = -1;
  for (int i = 0; i < m - 1; ++i) {
    if (s[i] < c) {
      cur_cov = i + m - 1;
    } else if (s[i] == c) {
      last_seen_c = i;
    }
  }
  for (int i = m - 1; i < s.size(); ++i) {
    if (s[i] < c)
      cur_cov = i + m - 1;
    else if (s[i] == c) {
      last_seen_c = i;
      if (cur_cov < i) {
        if (cnt > 0)
          --cnt;
        else
          return false;
        cur_cov = i + m - 1;
      }
    } else if (cur_cov < i) {
      if (last_seen_c + m - 1 >= i && cnt > 0) {
        --cnt;
        cur_cov = last_seen_c + m - 1;
      } else
        return false;
    }
  }
  return true;
}
int main() {
  int m;
  cin >> m;
  string s;
  cin >> s;
  string ss = s;
  sort(ss.begin(), ss.end());
  std::vector<int> cnt(ss.size());
  cnt[0] = 1;
  for (int i = 1; i < cnt.size(); ++i) {
    if (ss[i] == ss[i - 1])
      cnt[i] = cnt[i - 1] + 1;
    else
      cnt[i] = 1;
  }
  int top = ss.size(), bot = 0;
  while (top > bot) {
    int mid = (top + bot) / 2;
    if (check(s, ss[mid], cnt[mid], m))
      top = mid;
    else
      bot = mid + 1;
  }
  cout << ss.substr(0, top + 1) << endl;
  return 0;
}
