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 double eps = 1e-8;
const double pi = acos(-1.0);
const int mod = 1e9 + 7;
char s[100005];
int num[100005];
int sum[100005];
char ans[100005];
int main() {
  int m;
  scanf("%d %s", &m, s + 1);
  int n = strlen(s + 1);
  for (int i = 1; i <= n; i++) sum[s[i] - 'a']++;
  for (int i = 1; i <= n - m + 1;) {
    int j = i;
    char ch = s[i];
    int pos = i;
    while (j <= i + m - 1) {
      if (s[j] <= ch) {
        ch = s[j];
        pos = j;
      }
      j++;
    }
    num[ch - 'a']++;
    i = pos + 1;
  }
  int Max = 0;
  for (int i = 0; i < 26; i++) {
    if (num[i]) Max = i;
  }
  for (int i = 0; i < Max; i++) num[i] = sum[i];
  int cnt = 0;
  for (int i = 0; i < 26; i++) {
    for (int j = 0; j < num[i]; j++) ans[cnt++] = 'a' + i;
  }
  ans[cnt] = 0;
  printf("%s\n", ans);
  return 0;
}
