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 zi[30], m;
char a[110000];
int main() {
  cin >> m;
  scanf("%s", &a);
  for (int i = 0; i < strlen(a); ++i) zi[a[i] - 'a']++;
  for (char Maxa = 'a'; Maxa <= 'z'; ++Maxa) {
    int sum = 0, wei = -1, maywei = -1, i = 0;
    for (i = 0; i < strlen(a); ++i) {
      if (a[i] < Maxa)
        wei = i;
      else if (a[i] == Maxa)
        maywei = i;
      if (i - wei == m) {
        if (i - maywei < m) {
          sum++;
          wei = maywei;
        } else
          break;
      }
    }
    if (i == strlen(a)) {
      for (char r = 'a'; r < Maxa; ++r) cout << string(zi[r - 'a'], r);
      cout << string(sum, Maxa);
      break;
    }
  }
}
