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;
  vector<bool> sel(s.size());
  int last = -1;
  char maxch = 0;
  while (last + m < (int)s.size()) {
    auto it = min_element(s.rend() - 1 - (last + m), s.rend() - 1 - last);
    last = s.rend() - 1 - it;
    sel[last] = true;
    maxch = max(maxch, *it);
  }
  vector<int> indices;
  indices.reserve(s.size());
  for (size_t i = 0; i < s.size(); ++i) {
    if (sel[i] || s[i] < maxch) {
      indices.push_back(i);
    }
  }
  for (char ch = 'a'; ch <= 'z'; ++ch) {
    for (int index : indices) {
      if (s[index] == ch) {
        cout << ch;
      }
    }
  }
  cout << endl;
  return 0;
}
