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 ans[100010];
int vis[100010];
int main() {
  int n, tot = 0;
  cin >> n;
  string s;
  cin >> s;
  int st = 0;
  int len = s.length();
  char minn = 'a';
  while (st + n - 1 < len) {
    int k = st;
    char maxx = 'z' + 1;
    int maxid = 0;
    while (k < len && k < st + n) {
      if (maxx >= s[k]) {
        maxx = s[k];
        maxid = k;
      }
      k++;
    }
    ans[tot++] = s[maxid];
    vis[maxid] = 1;
    minn = max(s[maxid], minn);
    st = maxid + 1;
  }
  for (int i = 0; i < s.length(); i++)
    if (!vis[i] && s[i] < minn) ans[tot++] = s[i];
  sort(ans, ans + tot);
  printf("%s\n", ans);
}
