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>
const int N = 100005;
using namespace std;
char s[N];
int f[N], q[N], c[30];
int main() {
  int m, l, i, j, k;
  scanf("%d", &m);
  scanf("%s", s);
  l = strlen(s);
  s[l] = 'A';
  int h, t;
  for (i = 0; i < 26; i++) {
    int cnt = 0;
    bool ok = true;
    for (j = 0; j <= l; j++) {
      if (cnt >= m) ok = false;
      if (s[j] <= i + 'a')
        cnt = 0;
      else
        cnt++;
      if (s[j] == i + 'a') c[i]++;
    }
    if (cnt >= m) ok = false;
    if (!ok) continue;
    cnt = 0;
    c[i] = 0;
    for (j = 0; j <= l; j++) {
      if (s[j] < i + 'a') {
        if (cnt >= m) {
          int l = j - cnt, r = j - 1;
          h = 0;
          t = 0;
          for (k = l; k <= l + m - 1; k++)
            if (s[k] == i + 'a') {
              f[k] = 1;
              q[t++] = k;
            }
          for (; k < j; k++) {
            if (q[h] < k - m) h++;
            if (s[k] == i + 'a') {
              f[k] = f[q[h]] + 1;
              while (t > h && f[k] < f[q[t - 1]]) t--;
              q[t++] = k;
            }
          }
          int res = -1;
          for (k = j - 1; k >= j - m; k--)
            if (s[k] == i + 'a' && (res == -1 || f[k] < res)) res = f[k];
          c[i] += res;
        }
        cnt = 0;
      } else
        cnt++;
    }
    break;
  }
  for (i = 0; i < 26; i++)
    for (j = 0; j < c[i]; j++) printf("%c", i + 'a');
  return 0;
}
