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;
int m, lu, i, p, po, j, mr;
char in, st[100010];
bool mrk[100010], ok;
int main() {
  ifstream f("a.in");
  ofstream g("a.out");
  cin >> m;
  cin >> st;
  if (m == 1) {
    lu = strlen(st);
    sort(st, st + lu);
    cout << st;
  } else {
    lu = strlen(st);
    for (in = 'a'; in <= 'z'; ++in) {
      ok = true;
      p = 0;
      mr = 0;
      for (i = 0; i < m; ++i)
        if (st[i] == in) {
          mrk[i] = true;
          mr++;
        } else if (mrk[i])
          mr++;
      if (mr == 0) ok = false;
      j = 0;
      for (i = m; i < lu; ++i) {
        if (st[i] == in)
          mrk[i] = true, ++mr;
        else if (mrk[i])
          mr++;
        if (mrk[j]) --mr;
        ++j;
        if (mr == 0) ok = false;
      }
      if (ok) {
        for (i = 0; i < lu; ++i)
          if (st[i] == in) mrk[i] = false;
        p = 0;
        mr = 0;
        ok = false;
        for (i = 0; i < m; ++i)
          if (st[i] == in)
            p = i;
          else if (mrk[i])
            mr++;
        j = 0;
        for (i = m; i < lu; ++i) {
          if (st[i] == in)
            p = i;
          else if (mrk[i])
            mr++;
          if (mrk[j]) --mr;
          ++j;
          if (mr == 0) {
            ok = true;
            mrk[p] = true;
            if (p >= j) ++mr;
            cout << in;
          }
        }
        if (m == lu || !ok) cout << in;
        return 0;
      } else
        for (i = 0; i < lu; ++i)
          if (st[i] == in) cout << in;
    }
  }
  return 0;
}
