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 main() {
  int m;
  string s;
  cin >> m >> s;
  array<vector<int>, 'z' - 'a' + 1> positions;
  for (int i = 0; i < s.size(); ++i) positions[s[i] - 'a'].push_back(i);
  string ans;
  int curr_right = m - 1, curr_left = 0;
  while (curr_right < s.size()) {
    for (int i = 0; i < positions.size(); ++i) {
      if (positions[i].empty()) continue;
      vector<int>::iterator right;
      if (positions[i].size() == 1)
        right = positions[i].begin();
      else {
        right =
            upper_bound(positions[i].begin(), positions[i].end(), curr_right);
        if (right == positions[i].begin())
          continue;
        else
          right -= 1;
      }
      if (curr_left <= *right && *right <= curr_right) {
        curr_left = *right + 1;
        curr_right = *right + m;
        ans.push_back(i + 'a');
        break;
      } else
        continue;
    }
  }
  char max_c = 'a';
  for (char c : ans) max_c = max(max_c, c);
  size_t num_max_c = count(ans.begin(), ans.end(), max_c);
  for (int i = 0; i < max_c - 'a'; ++i)
    for (int j = 0; j < positions[i].size(); ++j) cout << char(i + 'a');
  for (int i = 0; i < num_max_c; ++i) cout << max_c;
  return 0;
}
