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;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
char A[100004];
int P[26];
int CNT[26];
int main() {
  int m;
  scanf("%d", &m);
  scanf("%s", A);
  int n = strlen(A);
  int st = 0, cnt = 0, l = 0;
  for (l = 0; l <= 25; l++) {
    st = 0, cnt = 0;
    for (; st <= n - m; st++) {
      int i = st;
      for (int j = 0; j <= l; j++) P[j] = -1;
      while (i < n && i < st + m) P[A[i] - 'a'] = i++;
      st = -1;
      for (int j = 0; j < l; j++) st = max(st, P[j]);
      if (st == -1) {
        if (P[l] == -1)
          break;
        else
          st = P[l], cnt++;
      }
    }
    if (st != -1) break;
  }
  for (int i = 0; i < n; i++) CNT[A[i] - 'a']++;
  for (int i = 0; i < l; i++)
    for (int j = 0; j < CNT[i]; j++) printf("%c", i + 'a');
  for (int i = 0; i < cnt; i++) printf("%c", l + 'a');
  printf("\n");
  return 0;
}
