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 main() {
  int m;
  string s;
  cin >> m;
  cin >> s;
  set<int> added;
  set<int> addedc;
  set<int>::iterator it;
  int n = s.size();
  string f = "";
  char max = 'a';
  for (int i = 0; i < n - m + 1;) {
    char c = s[i];
    int pos = i;
    for (int k = i + 1; k < i + m; ++k) {
      if (c >= s[k]) {
        c = s[k];
        pos = k;
      }
    }
    added.insert(pos);
    if (c >= max) max = c;
    i = pos + 1;
  }
  for (int i = 0; i < n; i++) {
    if (added.find(i) == added.end() && s[i] < max) f = f + s[i];
  }
  while (!added.empty()) {
    it = added.begin();
    f = f + s[*it];
    added.erase(it);
  }
  sort(f.begin(), f.end());
  cout << f;
}
