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 Maxn = 100020;
char s[Maxn];
int ls, m;
int nxt[Maxn];
bool check(int cs) {
  int last = -1;
  for (int i = 0; i < ls; i++) {
    if ((s[i] - 'a') <= cs) {
      last = i;
      continue;
    }
    if (i - last >= m) {
      return 0;
    }
  }
  return 1;
}
int main() {
  scanf("%d", &m);
  scanf("%s", s);
  ls = strlen(s);
  string rep;
  int cs = -1;
  for (int i = 0; i < 26; i++) {
    if (!check(i))
      ;
    else {
      cs = i;
      break;
    }
  }
  nxt[ls - 1] = ls;
  for (int i = ls - 2; i >= 0; i--) {
    if (s[i + 1] <= (cs + 'a'))
      nxt[i] = i + 1;
    else
      nxt[i] = nxt[i + 1];
  }
  int last = -1;
  for (int i = 0; i < ls; i++) {
    if (s[i] < cs + 'a') {
      rep.push_back(s[i]);
      last = i;
      continue;
    }
    if (s[i] > cs + 'a') continue;
    if (nxt[i] - last - 1 >= m) {
      last = i;
      rep.push_back(s[i]);
    }
  }
  sort(rep.begin(), rep.end());
  cout << rep << endl;
  return 0;
}
