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 int N = 1e5 + 5;
int v[30];
char s[N];
int m;
int main() {
  scanf("%d", &m);
  scanf("%s", s + 1);
  int len = strlen(s + 1);
  char maxc = 'a';
  for (int i = 1; i <= len - m + 1; ++i) {
    char u = 'z';
    int nextpos = -1;
    for (int j = i; j <= i + m - 1; ++j) {
      if (s[j] <= u) {
        u = s[j];
        nextpos = j;
      }
    }
    if (nextpos != -1) {
      v[u - 'a']++;
      s[nextpos] = '.';
      if (u > maxc) maxc = u;
      i = nextpos;
    }
  }
  for (int i = 1; i <= len; ++i) {
    if (s[i] != '.' && s[i] < maxc) v[s[i] - 'a']++;
  }
  for (int i = 0; i < 26; ++i) {
    while (v[i]--) {
      printf("%c", i + 'a');
    }
  }
  printf("\n");
  return 0;
}
