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 int lmt = 100005;
bool picked[lmt];
struct compare {
  bool operator()(pair<char, int> a, pair<char, int> b) const {
    if (a.first != b.first) return (a.first < b.first);
    return (a.second > b.second);
  }
};
set<pair<char, int>, compare> sett;
int main() {
  memset(picked, 0, sizeof(picked));
  string s;
  int m;
  cin >> m;
  cin >> s;
  int n = s.size();
  int last = (int)1e8;
  int st = 0, en = min(n - 1, m - 1);
  for (int i = st; i <= en; i++) sett.insert({s[i], i});
  while (en < n) {
    if (st <= last && last <= en) {
      sett.erase({s[st], st});
      if ((en + 1) < n) sett.insert({s[en + 1], en + 1});
      st++;
      en++;
      continue;
    }
    int chosen = sett.begin()->second;
    picked[chosen] = true;
    last = chosen;
    sett.erase({s[st], st});
    if ((en + 1) < n) sett.insert({s[en + 1], en + 1});
    st++;
    en++;
  }
  char largest = 'a';
  for (int i = 0; i < n; i++) {
    if (picked[i]) largest = max(largest, s[i]);
  }
  for (int i = 0; i < n; i++) {
    if (!picked[i] && s[i] < largest) picked[i] = true;
  }
  string ans = "";
  for (int i = 0; i < n; i++) {
    if (picked[i]) ans += s[i];
  }
  sort(ans.begin(), ans.end());
  cout << ans << "\n";
  return 0;
}
