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>
template <class T>
inline void rd(T &x) {
  char c = getchar();
  x = 0;
  while (!isdigit(c)) c = getchar();
  while (isdigit(c)) {
    x = x * 10 + c - '0';
    c = getchar();
  }
}
using namespace std;
const int inf = 0x3f3f3f3f;
const int mod = 1e9 + 7;
const int N = 1e5 + 10;
char s[N];
int ans[30];
int main() {
  int n, m;
  scanf("%d%s", &m, s + 1);
  n = strlen(s + 1);
  char p;
  for (p = 'a'; p <= 'z'; p++) {
    int tmp = 0;
    bool f = 1;
    for (int i = 1; i <= n; i++) {
      tmp++;
      if (s[i] <= p) tmp = 0;
      if (tmp >= m) {
        f = 0;
        break;
      }
    }
    if (!f) continue;
    break;
  }
  int tmp = 0;
  for (int i = 1; i <= n; i++) {
    tmp++;
    if (s[i] < p) {
      tmp = 0;
      ans[s[i] - 'a']++;
    } else if (s[i] == p) {
      int j;
      for (j = 0; j < m - tmp; j++) {
        if (s[j + i + 1] <= p) break;
      }
      if (j == m - tmp) {
        tmp = 0;
        ans[p - 'a']++;
      }
    }
  }
  for (int i = 0; i < 26; i++) {
    for (int j = 0; j < ans[i]; j++) printf("%c", i + 'a');
  }
  printf("\n");
  return 0;
}
