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() {
  vector<int> strr(26, 0);
  vector<int> curr(26, 0);
  vector<int> ind(26, 0);
  int m;
  string x;
  cin >> m >> x;
  int lastSelected = -1, done = -1;
  int minsofar = 26, maxsofar = -1;
  for (int j = 0; j < x.length(); j++) {
    curr[x[j] - 'a']++;
    ind[x[j] - 'a'] = j;
    if (lastSelected + m == j) {
      minsofar = 26;
      for (int i = 0; i < 26; i++) {
        if (curr[i] > 0) {
          maxsofar = max(maxsofar, i);
          strr[i]++;
          lastSelected = ind[i];
          break;
        }
      }
      for (int i = done + 1; i <= lastSelected; i++) {
        curr[x[i] - 'a']--;
      }
      done = lastSelected;
    }
  }
  for (int i = 0; i < 26; i++) ind[i] = 0;
  for (int j = 0; j < x.length(); j++) {
    ind[x[j] - 'a']++;
  }
  for (int i = 0; i < 26; i++) {
    if (i >= maxsofar) {
      for (int j = 0; j < strr[i]; j++) cout << (char)(i + 'a');
    } else {
      for (int j = 0; j < ind[i]; j++) cout << (char)(i + 'a');
    }
  }
  cout << endl;
  return 0;
}
