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;
  cin >> m;
  string s;
  cin >> s;
  int letters[s.length()];
  for (int i = 0; i < s.length(); i++) {
    letters[i] = (int)s[i] - 'a';
  }
  int n = s.length();
  int i = 0;
  bool check = true;
  while (check) {
    check = false;
    vector<int> test;
    test.push_back(-1);
    for (int j = 0; j < n; j++) {
      if (letters[j] <= i) test.push_back(j);
    }
    test.push_back(n);
    for (int k = 1; k < test.size(); k++) {
      if (test[k] - test[k - 1] > m) {
        check = true;
      }
    }
    i++;
  }
  i--;
  vector<pair<int, int> > compute;
  compute.push_back(make_pair(-1, 0));
  for (int j = 0; j < n; j++) {
    if (letters[j] <= i) compute.push_back(make_pair(j, letters[j]));
  }
  compute.push_back(make_pair(n, 0));
  int counts[i + 1];
  for (int k = 0; k < i + 1; k++) counts[k] = 0;
  for (int k = 1; k < compute.size() - 1; k++) {
    counts[compute[k].second]++;
  }
  for (int k = 1; k < compute.size() - 1; k++) {
    if (compute[k].second == i and
        compute[k + 1].first - compute[k - 1].first <= m) {
      counts[i]--;
      compute[k].first = compute[k - 1].first;
    }
  }
  for (int k = 0; k < i + 1; k++) {
    for (int l = 0; l < counts[k]; l++) {
      char c = (k + 'a');
      cout << ("%c", c);
    }
  }
  cout << endl;
  return 0;
}
