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;
char status[27], sample[100004];
map<char, int> stat;
int main() {
  status[1] = 'a';
  for (int i = 2; i <= 26; i++) status[i] = status[i - 1] + 1;
  int m;
  while (cin >> m) {
    for (int i = 1; i <= 26; i++) stat[status[i]] = 0;
    scanf("%s", sample);
    int len = strlen(sample), sc = 1, last = 0;
    for (int i = 0; i < len; i++) {
      stat[sample[i]]++;
    }
    for (int i = 0; i < len - m + 1;) {
      int Pos = i;
      char tempC = sample[i];
      for (int j = i + 1; j < i + m; j++) {
        if (sample[j] <= tempC) {
          Pos = j;
          tempC = sample[j];
        }
      }
      while (status[sc] < sample[Pos]) sc++, last = 0;
      if (sample[Pos] == status[sc]) last++;
      i = Pos + 1;
    }
    for (int i = 1; i < sc; i++)
      for (int j = 0; j < stat[status[i]]; j++) putchar(status[i]);
    for (int i = 0; i < last; i++) putchar(status[sc]);
    cout << endl;
  }
  return 0;
}
