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 cnt[26] = {};
string s;
char small() {
  for (int i = 0; i < 26; i++) {
    if (cnt[i] != 0) {
      return char(i + 97);
    }
  }
}
int index(int l, int r, char e) {
  for (int i = r - 1; i >= l; i--) {
    if (s[i] == e) return i;
  }
}
int main() {
  int m;
  cin >> m;
  cin >> s;
  vector<char> v;
  int l = s.length();
  int in = INT_MIN;
  int mi = INT_MAX;
  for (int i = 0; i < m; i++) {
    int x = s[i] - 97;
    cnt[x]++;
  }
  char e = small();
  in = index(0, m, e);
  v.push_back(e);
  int i = 1;
  while (i <= l - m) {
    cnt[int(s[i - 1]) - 97]--;
    cnt[int(s[i + m - 1]) - 97]++;
    int r = v.size();
    char e = small();
    if (e == v[r - 1]) {
      cnt[int(s[i + m - 1]) - 97]--;
      if (cnt[int(e) - 97] > 0) {
        if (in < i) {
          v.push_back(e);
          in = index(i, i + m, e);
        }
        cnt[int(s[i + m - 1]) - 97]++;
      } else {
        cnt[int(s[i + m - 1]) - 97]++;
        in = index(i, i + m, e);
        v.push_back(e);
      }
    } else {
      in = index(i, i + m, e);
      v.push_back(e);
    }
    i++;
  }
  memset(cnt, 0, sizeof(cnt));
  for (int i = 0; i < l; i++) {
    int x = s[i] - 97;
    cnt[x]++;
  }
  sort(v.begin(), v.end());
  for (int j = 0; j < v.size(); j++) {
    int x = int(v[j]) - 97;
    cnt[x]--;
  }
  int q = v.size();
  char d = v[q - 1];
  int st = d - 97;
  for (int i = 0; i < st; i++) {
    for (int j = 0; j < cnt[i]; j++) {
      v.push_back(char(i + 97));
    }
  }
  sort(v.begin(), v.end());
  for (int j = 0; j < v.size(); j++) cout << v[j];
}
