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;
const int MOD = 1e9 + 7;
const int MAX = 1e5 + 5;
int arr[MAX], n, m;
string s;
bool okay() {
  int dist = 0;
  for (int i = 0; i < n; i++) {
    if (arr[i])
      dist = 0;
    else
      dist++;
    if (dist >= m) return 0;
  }
  return 1;
}
int main() {
  cin >> m;
  cin >> s;
  n = s.size();
  for (int i = 0; i < 26; i++) {
    for (int j = 0; j < n; j++) {
      if (s[j] - 'a' == i) {
        arr[j] = 1;
      }
    }
    if (!okay()) continue;
    for (int j = 0; j < n; j++) {
      if (s[j] - 'a' == i) {
        arr[j] = 0;
      }
    }
    int dist = 0, last = -1;
    for (int j = 0; j < n; j++) {
      if (arr[j])
        dist = 0;
      else
        dist++;
      if (s[j] - 'a' == i) {
        last = j;
      }
      if (dist >= m) {
        arr[last] = 1;
        dist = j - last;
        last = -1;
      }
    }
    break;
  }
  vector<char> ret;
  for (int i = 0; i < n; i++)
    if (arr[i]) ret.push_back(s[i]);
  sort(ret.begin(), ret.end());
  for (int i = 0; i < ret.size(); i++) cout << ret[i];
}
