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 n, m;
int Q[100005], cnt[26];
char str[100005];
int main() {
  scanf("%d %s", &m, str);
  n = strlen(str);
  int L = 0, R = 0, i = 0, l = -m;
  while (i < n) {
    while (L < R && Q[L] < i) L++;
    for (int j = l + m; j < i + m; j++) {
      while (L < R && str[Q[R - 1]] >= str[j]) R--;
      Q[R++] = j;
    }
    cnt[str[Q[L]] - 'a']++;
    if (Q[L] + m >= n) break;
    l = i, i = Q[L] + 1;
  }
  for (i = 25; i >= 0; i--)
    if (cnt[i]) break;
  sort(str, str + n);
  for (int j = 0; j < n; j++) {
    putchar(str[j]);
    if (str[j] == i + 'a' && --cnt[i] == 0) break;
  }
  return 0;
}
