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;
const int INF = 1e9;
const long long int INFF = 1e17;
const double EPS = 1e-9;
const long long int MOD = 1e9 + 7;
const int MAXN = 1e5 + 10;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n, m;
  bool mark[MAXN];
  char curr;
  string s, ans = "";
  cin >> m;
  cin >> s;
  n = s.length();
  for (int i = (0); i < (n); ++i) mark[i] = 0;
  for (int i = (0); i < (26); ++i) {
    curr = i + 'a';
    int start = 0;
    bool flag = 0;
    string tmp1 = "", tmp2 = "";
    while (start < (n - m + 1)) {
      int ma = -1;
      for (int j = start + m - 1; j >= start; j--)
        if (s[j] == curr) {
          if (!mark[start]) {
            tmp1 += curr;
            ma = j;
            break;
          }
        }
      if (ma != -1) {
        for (int j = (start); j < (ma + 1); ++j) mark[j] = 1;
        start = ma + 1;
      } else
        start++;
    }
    for (int j = (0); j < (n - m + 1); ++j)
      if (!mark[j]) flag = 1;
    if (!flag) {
      ans += tmp1;
      break;
    } else {
      for (int j = (0); j < (n); ++j)
        if (s[j] == curr) tmp2 += curr;
      ans += tmp2;
    }
  }
  cout << ans << '\n';
  return 0;
}
