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 main() {
  ios::sync_with_stdio(false);
  ;
  long long i, j, k, l, r, m, n, o, t;
  {
    char str[100001];
    bool mark[100000] = {0};
    long long alpha[26] = {0};
    cin >> m;
    cin >> str;
    l = strlen(str);
    for (i = 0; i < l; i++) alpha[str[i] - 'a']++;
    long long coun = 0;
    for (i = 0; i < 26; i++) {
      long long al = 'a' + i;
      bool flag = 1;
      for (j = 0; j <= l - m; j++) {
        bool fla = 0;
        for (k = j; k <= j + m - 1; k++) {
          if (mark[k] == 1 || str[k] == al) {
            fla = 1;
            break;
          }
        }
        if (fla == 0) {
          flag = 0;
          break;
        } else {
          j = k;
        }
      }
      if (flag) {
        for (j = 0; j <= l - m; j++) {
          bool flag = 1;
          for (k = j + m - 1; k >= j; k--) {
            if (mark[k] == 1) {
              flag = 0;
              j = k;
              break;
            }
          }
          if (flag) {
            for (k = j + m - 1; k >= j; k--) {
              if (str[k] == al) {
                coun++;
                j = k;
                break;
              }
            }
          }
        }
        break;
      } else {
        for (j = 0; j < l; j++)
          if (str[j] == al) mark[j] = 1;
      }
    }
    for (j = 0; j < i; j++) {
      for (k = 0; k < alpha[j]; k++) {
        cout << (char)('a' + j);
      }
    }
    for (k = 0; k < coun; k++) cout << (char)('a' + i);
    cout << endl;
  }
}
