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 ok[200000] = {};
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  string ans;
  for (int i = 'a'; i <= 'z'; ++i) {
    string pre_ans;
    for (int q = 0; q < s.length(); ++q) {
      if ((int)s[q] == i) {
        pre_ans.push_back(s[q]);
        ok[q] = true;
      }
    }
    int cnt = 0;
    for (int j = 0; j < s.length(); ++j) {
      if (ok[j] == false) {
        cnt++;
      } else {
        if (cnt >= n) goto failed_system_test;
        cnt = 0;
      }
    }
    if (cnt >= n) goto failed_system_test;
    sort(ans.begin(), ans.end());
    cout << ans;
    for (int j = 0; j < s.length(); ++j) {
      if ((int)s[j] == i) {
        int winner = 1;
        for (int p = j - 1; p >= 0; --p) {
          if (ok[p] == false)
            winner++;
          else
            break;
        }
        for (int p = j + 1; p < s.length(); ++p) {
          if (ok[p] == false)
            winner++;
          else
            break;
        }
        if (winner >= n) {
          cout << (char)i;
        } else
          ok[j] = false;
      }
    }
    cout << endl;
    return 0;
  failed_system_test:;
    ans += pre_ans;
  }
}
