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 tab[30];
int wziete[30];
int pojawione[30];
int suma[30];
int litery[100010];
bool czy[100010];
bool czydobrze;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  int n;
  string a;
  cin >> n;
  cin >> a;
  for (int i = 1; i <= a.size(); i++) {
    litery[i] = a[i - 1] - 'a';
    suma[litery[i]]++;
  }
  tab[0]++;
  for (int i = 1; i < n; i++) {
    pojawione[litery[i]] = i;
  }
  for (int i = n; i <= a.size(); i++) {
    pojawione[litery[i]] = i;
    if (czy[i - n] == 1) {
      czydobrze = 0;
    }
    if (czydobrze == 0) {
      int x = 0;
      while (pojawione[x] < i - n + 1) {
        x++;
      }
      czy[pojawione[x]] = 1;
      wziete[x]++;
      czydobrze = 1;
    }
  }
  int m = 0;
  for (int i = 0; i < 28; i++) {
    if (wziete[i]) {
      m = i;
    }
  }
  char c;
  for (int i = 0; i < m; i++) {
    c = i + 'a';
    for (int j = 0; j < suma[i]; j++) {
      cout << c;
    }
  }
  c = m + 'a';
  for (int i = 0; i < wziete[m]; i++) {
    cout << c;
  }
  return 0;
}
