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;
char str[100005];
vector<char> ans;
int main() {
  int m;
  scanf("%d", &m);
  scanf("%s", str);
  int len = (int)strlen(str);
  char tmp = 'a' - 1;
  int t = 0, i, pos;
  for (i = 0; i + m - 1 < len;) {
    pos = -1;
    char ch = '\0';
    for (int j = i; j < i + m; j++) {
      if (pos == -1) {
        ch = str[j], pos = j;
      } else if (ch > str[j]) {
        ch = str[j];
        pos = j;
      } else if (ch == str[j]) {
        pos = j;
      }
    }
    i = pos + 1;
    if (tmp < ch)
      tmp = ch, t = 1;
    else if (tmp == ch) {
      t++;
    }
  }
  while (t--) ans.push_back(tmp);
  for (int i = 0; i < len; i++) {
    if (str[i] < tmp) ans.push_back(str[i]);
  }
  sort(ans.begin(), ans.end());
  for (int i = 0; i < ans.size(); i++) {
    printf("%c", ans[i]);
  }
  putchar('\n');
}
