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>
int main() {
  std::ios_base::sync_with_stdio(false);
  long m;
  std::cin >> m;
  std::string s;
  std::cin >> s;
  long count[26] = {};
  for (int j = 'a'; j <= 'z'; ++j) {
    long max_len = 0;
    long len = 0;
    for (long i = 0; i != (long)s.size(); ++i) {
      if (s[i] > j) {
        max_len = std::max(max_len, ++len);
        continue;
      }
      if (s[i] == j) ++count[j - 'a'];
      len = 0;
    }
    if (max_len < m) {
      long last = 0;
      long len = 0;
      count[j - 'a'] = 0;
      for (long i = 0; i != (long)s.size(); ++i) {
        if (s[i] < j) {
          len = 0;
          continue;
        }
        ++len;
        if (s[i] == j) last = i;
        if (len == m) {
          ++count[j - 'a'];
          len = i - last;
        }
      }
      break;
    }
  }
  for (int i = 0; i != 'z' - 'a' + 1; ++i)
    for (long j = 0; j != count[i]; ++j) std::cout << (char)(i + 'a');
  std::cout << "\n";
  return 0;
}
