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>
const int N = 1e5 + 10;
int n, m, a[N];
char s[N];
bool solve(char x) {
  int res = 0, pre = 0, flag = 0;
  for (int i = 1; i <= n; i++) {
    if (a[i]) {
      if (res ^ pre && i - pre <= m) a[res] = 0;
      pre = res = i;
    }
    if (s[i] == x) {
      if (res ^ pre && i - pre <= m)
        a[res] = 0, a[i] = 1, res = i;
      else
        a[i] = 1, pre = res, res = i;
    } else if (i - res >= m)
      flag = 1;
  }
  if (!flag) {
    if (res ^ pre && n - pre < m) a[res] = 0;
    for (int i = 1; i <= n; i++)
      if (s[i] == x && a[i]) putchar(x);
    return true;
  } else {
    for (int i = 1; i <= n; i++)
      if (s[i] == x) putchar(x), a[i] = 1;
    return false;
  }
}
int main() {
  scanf("%d%s", &m, s + 1), n = strlen(s + 1);
  for (int i = 0; i < 26; i++)
    if (solve('a' + i)) return 0;
}
