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;
vector<int> check(const vector<vector<int>> &mas, const vector<int> &answer,
                  const int &index, bool &flag, const string &s, const int &m) {
  vector<int> result = answer;
  for (int i = 0; i < mas[index].size(); i++) result.push_back(mas[index][i]);
  result.push_back(-1);
  result.push_back(s.length());
  sort(result.begin(), result.end());
  for (int i = 0; i < result.size() - 1; i++) {
    if (result[i] + m < result[i + 1]) {
      return result;
    }
  }
  flag = true;
  return answer;
}
int main() {
  int m;
  cin >> m;
  string s;
  cin >> s;
  vector<vector<int>> mas(26);
  vector<int> answer;
  vector<bool> used(s.length(), true);
  bool flag = false;
  for (int i = 0; i < s.length(); i++) mas[int(s[i]) - int('a')].push_back(i);
  for (int i = 0; i < 26; i++) {
    answer = check(mas, answer, i, flag, s, m);
    if (flag == true) {
      if (!answer.empty()) {
        for (int j = 0; j < s.length() - m + 1; j++) {
          auto it = lower_bound(answer.begin(), answer.end(), j + m);
          it--;
          if (*it >= j && *it <= j + m - 1)
            continue;
          else
            used[j] = false;
        }
      } else {
        used.clear();
        used.resize(s.length(), false);
      }
      for (int j = 0; j < s.length() - m + 1; j++) {
        if (used[j] == false) {
          auto it = lower_bound(mas[i].begin(), mas[i].end(), j + m);
          it--;
          answer.push_back(*it);
          j = *it;
        }
      }
      break;
    }
  }
  vector<char> ans;
  for (int i = 0; i < answer.size(); i++) {
    if (answer[i] != -1 && answer[i] != s.length()) ans.push_back(s[answer[i]]);
  }
  sort(ans.begin(), ans.end());
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i];
  }
  return 0;
}
