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>
int n, m;
char s[100010];
int cont[110];
int v[100010];
void f() {
  int l = 0, k = 0;
  char b = 'a';
  for (int i = 0; i < n && i < n - m + 1; i++) {
    k = 0;
    char a = 'z';
    for (int j = i; j < m + i; j++) {
      if (s[j] < b) {
        k = j;
        break;
      }
      if (s[j] <= a) {
        a = s[j];
        k = j;
      }
    }
    if (s[k] > b) b = s[k];
    cont[s[k] - 'a']++;
    v[k] = 1;
    i = k;
  }
  for (int i = 0; i < n; i++) {
    if (s[i] < b && !v[i]) cont[s[i] - 'a']++;
  }
  for (int i = 0; i < 26; i++) {
    while (cont[i]) {
      char x = i + 'a';
      printf("%c", x);
      cont[i]--;
    }
  }
  puts("");
}
int main() {
  scanf("%d%s", &m, s);
  memset(cont, 0, sizeof(cont));
  memset(v, 0, sizeof(v));
  n = strlen(s);
  if (n <= m) {
    char a = 'z';
    for (int i = 0; i < n; i++) {
      if (s[i] < a) a = s[i];
    }
    printf("%c\n", a);
    return 0;
  }
  f();
  return 0;
}
