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 M;
bool cover(const string str, vector<char>& used, char smallest) {
  int len = ((int)str.size());
  int life = M;
  for (int i = 0; i < (int)(len); ++i) {
    if (used[i] || str[i] == smallest)
      life = M;
    else
      life -= 1;
    if (life == 0) return false;
  }
  auto covered = used;
  life = M;
  int candidate = -1;
  for (int i = 0; i < (int)(len); ++i) {
    if (covered[i]) {
      life = M;
    } else if (str[i] == smallest) {
      if (life == 1) {
        used[i] = smallest;
        life = M;
      } else {
        candidate = i;
        --life;
      }
    } else {
      --life;
      if (life == 0) {
        used[candidate] = smallest;
        i = candidate;
        life = M;
      }
    }
  }
  return true;
}
int main(void) {
  cin.sync_with_stdio(false);
  cin >> M;
  string str;
  cin >> str;
  vector<char> used(((int)str.size()), 0);
  char smallest = 'a';
  while (true) {
    if (cover(str, used, smallest)) {
      break;
    } else {
      for (int i = 0; i < (int)(((int)str.size())); ++i) {
        if (str[i] == smallest) {
          used[i] = smallest;
        }
      }
      smallest += 1;
    }
  }
  vector<char> ans;
  for (int i = 0; i < (int)(((int)str.size())); ++i) {
    if (used[i]) ans.push_back(used[i]);
  }
  sort((ans).begin(), (ans).end());
  for (auto ch : ans) cout << ch;
  cout << endl;
  return 0;
}
