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;
int vis[100005];
string ans;
int cnt[27];
int main() {
  int n, m;
  string s;
  cin >> m >> s;
  n = s.size();
  for (int i = int(0); i <= int(n - 1); i++) cnt[s[i] - 'a']++;
  for (int j = int(0); j <= int(25); j++) {
    int mx = -1, prev = -1;
    char ch = j + 'a';
    vector<int> v;
    bool flag = true;
    for (int i = int(0); i <= int(n - 1); i++) {
      if (s[i] == ch) mx = i;
      if (vis[i]) prev = i;
      if (i - m >= prev) {
        prev = mx;
        if (i - m >= prev) {
          for (int k = int(0); k <= int(cnt[j] - 1); k++) {
            ans += ch;
          }
          for (int i = int(0); i <= int(n - 1); i++) {
            if (s[i] == ch) vis[i] = 1;
          }
          flag = false;
          break;
        } else {
          v.push_back(mx);
        }
      }
    }
    if (flag)
      for (int i = int(0); i <= int(v.size() - 1); i++) {
        vis[v[i]] = 1;
        ans += s[v[i]];
      }
  }
  cout << ans << endl;
  return 0;
}
