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 long long MAXN = 5000 + 7;
const long long MOD = 1e9 + 7;
char s[100010];
int ans;
int main() {
  int n;
  scanf("%d", &n);
  scanf("%s", s);
  int len = strlen(s);
  for (int i = 0; i < 26; i++) {
    int cnt = 0;
    int flag = 0;
    for (int j = 0; j < len; j++) {
      if (s[j] - 'a' <= i) {
        cnt = 0;
      } else
        cnt++;
      if (cnt == n) break;
      if (j == len - 1) flag = 1;
    }
    if (flag == 1) {
      ans = i;
      break;
    }
  }
  int mp[40] = {0};
  int outt = 0;
  int c = 0;
  int max1 = 0;
  for (int i = 0; i < len; i++) {
    mp[s[i] - 'a']++;
    if (s[i] - 'a' < ans) {
      c = 0;
    } else {
      c++;
      if (s[i] - 'a' == ans) max1 = i;
      if (c == n) {
        c = i - max1;
        outt++;
      }
    }
  }
  for (int i = 0; i < ans; i++) {
    for (int j = 1; j <= mp[i]; j++) {
      printf("%c", i + 'a');
    }
  }
  for (int i = 1; i <= outt; i++) {
    printf("%c", ans + 'a');
  }
}
