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;
vector<int> c[26];
string S;
int n;
tuple<char, int, int> d[120000];
int main() {
  cin >> n >> S;
  for (int i = 0; i < S.size(); i++) {
    c[S[i] - 'a'].push_back(i);
  }
  int maxn = 0;
  for (int i = 0; i <= S.size() - n; i++) {
    for (int j = 0; j < 26; j++) {
      int pos1 = lower_bound(c[j].begin(), c[j].end(), i) - c[j].begin();
      int pos2 = lower_bound(c[j].begin(), c[j].end(), i + n) - c[j].begin();
      if (pos1 == pos2) continue;
      d[i] = make_tuple('a' + j, c[j][pos1], c[j][pos2 - 1]);
      maxn = max(maxn, j);
      break;
    }
  }
  string ans = "";
  for (int i = 0; i < maxn; i++) {
    for (int j = 0; j < c[i].size(); j++) ans += ('a' + i);
  }
  int G = -1;
  for (int i = 0; i <= S.size() - n; i++) {
    if (get<0>(d[i]) == ('a' + maxn)) {
      if (get<1>(d[i]) <= G) continue;
      ans += ('a' + maxn);
      G = get<2>(d[i]);
    }
  }
  cout << ans << endl;
  return 0;
}
