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() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int m;
  cin >> m;
  string s;
  cin >> s;
  for (char c = 'a'; c <= 'z'; ++c) {
    vector<int> get;
    int lastPossibleChar = -1;
    int lastIndex = -1;
    bool found = true;
    for (int i = 0; i < (int)s.size(); ++i) {
      if (s[i] < c) {
        lastIndex = i;
      } else if (s[i] == c) {
        lastPossibleChar = i;
      }
      if (i - lastIndex >= m) {
        if (i - lastPossibleChar < m) {
          lastIndex = lastPossibleChar;
          get.push_back(lastPossibleChar);
        } else {
          found = false;
        }
      }
    }
    if (found) {
      string answer;
      for (int i = 0; i < (int)s.size(); ++i) {
        if (s[i] < c) {
          answer += s[i];
        } else if (binary_search(get.begin(), get.end(), i)) {
          answer += c;
        }
      }
      sort(answer.begin(), answer.end());
      cout << answer << endl;
      return 0;
    }
  }
  sort(s.begin(), s.end());
  cout << s << endl;
  return 0;
}
