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 main() {
  int m;
  scanf("%d", &m);
  char s[100005];
  scanf("%s", s);
  multiset<char> ans;
  multiset<char>::iterator it;
  int l = strlen(s);
  bool taken[l];
  memset(taken, false, sizeof(taken));
  char Max = 'a';
  int ind;
  for (int i = 0; i <= l - m; i++) {
    ind = i;
    for (int j = i + 1; j < i + m && j < l; j++)
      if (s[ind] >= s[j]) ind = j;
    if (s[ind] > Max) Max = s[ind];
    taken[ind] = true;
    ans.insert(s[ind]);
    i = ind;
  }
  for (int i = 0; i < l; i++)
    if (!taken[i] && s[i] < Max) ans.insert(s[i]);
  for (it = ans.begin(); it != ans.end(); ++it) cout << (*it);
  return 0;
}
