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;
char st[100005];
int n, m, a[100005], f[100005], g[100005];
int main() {
  int i, j, p, q;
  scanf("%d\n", &m);
  scanf("%s", st + 1);
  n = strlen(st + 1);
  for (i = 'a'; i <= 'z'; i++) {
    for (j = 1; j <= n; j++) a[j] = (st[j] == i);
    for (j = 1; j <= n; j++) g[j] = f[j] | a[j];
    p = 0, g[n + 1] = 1;
    for (j = 1; j <= n + 1; j++)
      if (g[j]) {
        if (j - p > m) break;
        p = j;
      }
    if (j <= n + 1) {
      for (j = 1; j <= n; j++) {
        if (a[j]) printf("%c", i);
        f[j] = g[j];
      }
      continue;
    } else {
      p = q = 0;
      for (j = 1; j <= n + 1; j++) {
        if (j - p > m) {
          p = q, q = 0;
          printf("%c", i);
        }
        if (f[j]) {
          p = j, q = 0;
        }
        if (a[j]) q = j;
      }
      return 0;
    }
  }
  return 0;
}
