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>
#pragma warning(disable : 4996)
using namespace std;
int k, len;
char s[100011];
bool token[100011];
char lastToken;
int main() {
  scanf("%d%s", &k, s);
  len = strlen(s);
  for (int i = 'a'; i <= 'z'; i++) {
    lastToken = char(i);
    for (int j = 0; j < len; j++)
      if (s[j] == char(i)) token[j] = 1;
    int l = 0;
    int last = -1e8;
    bool ok = true;
    for (int r = 0; r < len; r++) {
      if (token[r]) last = r;
      if (r - l < k - 1) continue;
      if (r - last > k - 1) {
        ok = false;
        break;
      }
      ++l;
    }
    if (ok) break;
  }
  for (int i = 0; i < len; i++) {
    if (lastToken == s[i]) token[i] = 0;
  }
  int l = 0;
  int last = -1e8, lastNeed = 0;
  for (int r = 0; r < len; r++) {
    if (token[r]) last = r;
    if (s[r] == lastToken) lastNeed = r;
    if (r - l < k - 1) continue;
    if (r - last > k - 1) {
      token[lastNeed] = 1;
      last = lastNeed;
    }
    ++l;
  }
  string ans = "";
  for (int i = 0; i < len; i++)
    if (token[i]) ans += s[i];
  sort(ans.begin(), ans.end());
  puts(ans.c_str());
  return 0;
}
