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 n, m;
char s[100010];
vector<int> pos[26];
set<int> st;
int main() {
  scanf("%d %s", &m, s);
  n = strlen(s);
  for (int i = 0; i < n; ++i) {
    pos[s[i] - 'a'].push_back(i);
  }
  for (int c = 0; c < 26; ++c) {
    int cnt = 0;
    bool ok = true;
    for (int i = n - 1; ok && i >= m - 1; --i) {
      set<int>::iterator it = st.lower_bound(i - m + 1);
      if (it != st.end() && *it <= i) {
        i = *it;
        continue;
      }
      vector<int>::iterator iit =
          lower_bound(pos[c].begin(), pos[c].end(), i - m + 1);
      if (iit != pos[c].end() && *iit <= i) {
        i = *iit;
        ++cnt;
        continue;
      } else {
        ok = false;
      }
    }
    if (ok) {
      for (int i = 0; i < c; ++i) {
        for (int j = 0; j < (int)pos[i].size(); ++j) {
          printf("%c", 'a' + i);
        }
      }
      for (int i = 0; i < cnt; ++i) {
        printf("%c", 'a' + c);
      }
      printf("\n");
      return 0;
    }
    for (int i = 0; i < (int)pos[c].size(); ++i) {
      st.insert(pos[c][i]);
    }
  }
  return 0;
}
