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;
string s1;
int n;
int sum[1 << 21];
void clean() {
  for (int i = 0; i <= n; i++) sum[i] = 0;
}
int get_sum(int index) {
  int tot = 0;
  while (index >= 1) {
    tot += sum[index];
    index = index - (index & (-index));
  }
  return tot;
}
void update(int index, int val) {
  while (index <= (100000 + 200)) {
    sum[index]++;
    index += index & (-index);
  }
}
int main() {
  int flag;
  int m;
  cin >> m;
  char p;
  cin >> s1;
  n = s1.size();
  s1 = '#' + s1;
  for (char x = 'a'; x <= 'z'; x++) {
    flag = 0;
    clean();
    for (int i = 1; i <= n; i++) {
      if (s1[i] <= x) sum[i]++;
    }
    for (int i = 1; i <= n; i++) sum[i] += sum[i - 1];
    for (int i = m; i <= n; i++)
      if (sum[i] - sum[i - m] == 0) {
        flag = 1;
        break;
      }
    if (flag == 0) {
      p = x;
      break;
    }
  }
  clean();
  for (int i = 1; i <= n; i++) {
    if (s1[i] < p) update(i, 1);
  }
  int counts = 0;
  for (int i = 1; i <= n; i++) {
    int st = i;
    int en = i + m - 1;
    if (en > n) break;
    int tot = get_sum(en) - get_sum(st - 1);
    if (tot == 0) {
      for (int j = i + m - 1; j >= i; j--) {
        if (s1[j] == p) {
          counts++;
          update(j, 1);
          break;
        }
      }
    }
  }
  vector<char> v;
  for (int i = 1; i <= n; i++)
    if (s1[i] < p) v.push_back(s1[i]);
  sort(v.begin(), v.end());
  for (int i = 0; i < v.size(); i++) cout << v[i];
  while (counts--) cout << p;
  return 0;
}
