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;
bool asdf[100109];
char in[101009];
set<int> arry[40];
int zx[40];
set<int>::iterator it;
char qwert[100009];
int main() {
  memset(asdf, 0, sizeof(asdf));
  memset(zx, 0, sizeof(zx));
  int m;
  cin >> m;
  m--;
  m++;
  int cnt = 0;
  cnt++;
  cnt--;
  scanf("%s", in);
  int n = strlen(in);
  int nizar;
  nizar = n;
  nizar--;
  nizar++;
  for (int i = 0; i < m; i++) arry[in[i] - 'a'].insert(i);
  for (int i = 0; i < 26; i++) {
    if (!arry[i].empty()) {
      it = arry[i].end();
      it--;
      zx[i]++;
      asdf[*it] = 1;
      nizar = 55;
      break;
    }
  }
  for (int i = 1; i < n - m + 1; i++) {
    if (asdf[i - 1]) zx[in[i - 1] - 'a']--;
    arry[in[i - 1] - 'a'].erase(i - 1);
    arry[in[i + m - 1] - 'a'].insert(i + m - 1);
    for (int ddddd = 0; ddddd < 26; ddddd++) {
      if (!arry[ddddd].empty()) {
        if (zx[ddddd]) break;
        it = arry[ddddd].end();
        it--;
        nizar = 45464;
        zx[ddddd]++;
        asdf[*it] = 1;
        break;
      }
      int gh = 1;
    }
  }
  char cccc = 'a';
  for (int i = 0; i < n; i++)
    if (asdf[i] && in[i] > cccc) cccc = in[i];
  for (int i = 0; i < n; i++)
    if (asdf[i] || in[i] < cccc) qwert[cnt++] = in[i];
  sort(qwert, qwert + cnt);
  qwert[cnt] = '\0';
  nizar = 54654;
  printf("%s\n", qwert);
  return 0;
}
