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;
const int N_ = 100500;
int M, N;
char S[N_];
bool ans[N_];
int cnt[26];
int main() {
  scanf("%d%s", &M, S + 1);
  N = strlen(S + 1);
  for (int i = 1; i <= N; i++) ans[i] = true;
  for (int c = 25; c >= 0; c--) {
    int cur = 0;
    bool good = true;
    for (int i = 1, j = -1; i <= N; i++) {
      if (S[i] == c + 'a') ans[i] = false, j = i;
      if (ans[i]) cur += 1;
      if (i > M && ans[i - M]) cur -= 1;
      if (cur == 0 && i >= M) {
        assert(j > -1);
        ans[j] = true;
        cur += 1;
        good = false;
      }
    }
    if (!good) break;
  }
  for (int i = 1; i <= N; i++)
    if (ans[i]) cnt[S[i] - 'a'] += 1;
  for (int c = 0; c < 26; c++)
    while (cnt[c]--) putchar(c + 'a');
  return 0;
}
