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;
const int MAX = 1e5 + 10;
int n, m, cnt[26], kt, f[MAX];
deque<int> que;
bool fr[26];
char s[MAX];
bool check() {
  int pos = 0;
  for (int i = 1; i <= n + 1; ++i)
    if (i == n + 1 || !fr[s[i] - 'a']) {
      if (i - m > pos) return false;
      pos = i;
    }
  return true;
}
int main() {
  scanf("%d %s", &m, s + 1);
  n = strlen(s + 1);
  for (int i = 1; i <= n; ++i) ++cnt[s[i] - 'a'];
  for (int digit = 25; digit >= 0; --digit)
    if (cnt[digit] > 0) {
      fr[digit] = true;
      if (!check()) {
        fr[digit] = false;
        kt = digit;
        break;
      }
      cnt[digit] = 0;
    }
  int j = 1;
  que.push_back(0);
  for (int i = 1; i <= n + 1; ++i)
    if (i == n + 1 || !fr[s[i] - 'a']) {
      while (!que.empty() && i - m > que.front()) que.pop_front();
      f[i] = f[que.front()];
      if (i <= n && s[i] - 'a' == kt) ++f[i];
      while (!que.empty() && f[i] < f[que.back()]) que.pop_back();
      que.push_back(i);
    }
  cnt[kt] = f[n + 1];
  for (int digit = 0; digit < 26; ++digit)
    for (int sz = 0; sz < cnt[digit]; ++sz) printf("%c", 'a' + digit);
  return 0;
}
