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;
bool IsGood(vector<int> &select, int b, int n) {
  if (select.size() == 0) {
    return false;
  }
  sort(select.begin(), select.end());
  if (select[0] >= b) {
    return false;
  }
  if (n - select.back() >= b) {
    return false;
  }
  for (int i = 0; i < select.size() - 1; ++i) {
    if (select[i + 1] - select[i] > b) {
      return false;
    }
  }
  return true;
}
void Update(string &str, vector<bool> &was, char c, int b) {
  int x1 = 0;
  while (true) {
    int last = -1;
    for (int i = x1; i < x1 + b; ++i) {
      if (i >= str.size()) {
        break;
      }
      if (str[i] == c) {
        last = i;
      }
      if (was[i]) {
        last = i;
        break;
      }
    }
    assert(last != -1);
    was[last] = true;
    x1 = last + 1;
    if (last + b - 1 >= str.size() - 1) {
      break;
    }
  }
}
int main(int argc, const char *argv[]) {
  std::ios::sync_with_stdio(false);
  int b;
  cin >> b;
  string str;
  cin >> str;
  vector<int> select;
  vector<bool> was(str.size(), false);
  for (char c = 'a'; c <= 'z'; ++c) {
    vector<int> selectOld = select;
    for (int i = 0; i < str.size(); ++i) {
      if (str[i] == c) {
        select.push_back(i);
      }
    }
    if (IsGood(select, b, str.size() - 1)) {
      for (int i = 0; i < selectOld.size(); ++i) {
        was[selectOld[i]] = true;
      }
      Update(str, was, c, b);
      break;
    }
  }
  vector<int> count('z' - 'a' + 1, 0);
  for (int i = 0; i < was.size(); ++i) {
    if (was[i]) {
      char k = str[i] - 'a';
      ++count[k];
    }
  }
  string res = "";
  for (int i = 0; i < count.size(); ++i) {
    res += string(count[i], char(i + 'a'));
  }
  cout << res << endl;
  return 0;
}
