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;
const long long MOD = 1000000007LL;
int main() {
  int m;
  cin >> m;
  string s;
  cin >> s;
  int najvec = 0;
  int num[26];
  memset(num, 0, sizeof(num));
  for (int i = 0, _n = s.length(); i < _n; i++) {
    if (i < m) {
      num[s[i] - 'a']++;
      if (i + 1 != s.length() && i + 1 != m) continue;
      int najmanj = 0;
      while (num[najmanj] == 0) najmanj++;
      if (najmanj > najvec) najvec = najmanj;
      continue;
    }
    num[s[i - m] - 'a']--;
    num[s[i] - 'a']++;
    int najmanj = 0;
    while (num[najmanj] == 0) najmanj++;
    if (najmanj > najvec) {
      najvec = najmanj;
    }
  }
  vector<char> out;
  for (int i = 0, _n = s.length(); i < _n; i++) {
    if (s[i] < 'a' + najvec) out.push_back(s[i]);
  }
  sort(out.begin(), out.end());
  for (int i = 0, _n = out.size(); i < _n; i++) cout << out[i];
  int st = 0;
  priority_queue<int> ggg;
  int zadnji = -1;
  for (int i = 0, _n = s.length(); i < _n; i++) {
    if (s[i] < 'a' + najvec) {
      zadnji = i;
      continue;
    }
    if (s[i] == 'a' + najvec) ggg.push(i);
    if (zadnji + m <= i) {
      st++;
      zadnji = ggg.top();
      ggg.pop();
    }
  }
  for (int i = 0, _n = st; i < _n; i++) cout << char('a' + najvec);
  cout << "\n";
  return 0;
}
