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;
struct coisa {
  char l;
  int p;
  coisa() {}
  coisa(char _l, int _p) {
    l = _l;
    p = _p;
  }
  bool operator<(const coisa &a) const {
    if (l == a.l) return p > a.p;
    return l < a.l;
  }
};
set<coisa> S;
int cnt[300];
pair<int, int> atual[300];
int main() {
  int i, m;
  char s[100005];
  scanf("%d", &m);
  scanf(" %s", s);
  for (i = 0; s[i]; i++) cnt[(int)s[i]]++;
  for (i = 0; i < m; i++) {
    S.insert(coisa(s[i], i));
  }
  for (int c = 'a'; c <= 'z'; c++) {
    atual[c].first = 0;
    atual[c].second = -1;
  }
  auto it = S.begin();
  char maxi = it->l;
  atual[(int)it->l].first++;
  atual[(int)it->l].second = it->p;
  for (; s[i]; i++) {
    S.erase(coisa(s[i - m], i - m));
    S.insert(coisa(s[i], i));
    it = S.begin();
    maxi = max(maxi, it->l);
    if ((atual[(int)it->l].second == -1) ||
        (i - atual[(int)it->l].second >= m)) {
      atual[(int)it->l].first++;
      atual[(int)it->l].second = it->p;
    }
  }
  for (char c = 'a'; c < maxi; c++) {
    for (i = 0; i < cnt[(int)c]; i++) printf("%c", c);
  }
  for (i = 0; i < atual[(int)maxi].first; i++) printf("%c", maxi);
  printf("\n");
  return 0;
}
