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 INFint = 2e9;
const long long INF = 2e18;
const int MOD = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(0);
  int m;
  string s;
  cin >> m >> s;
  string ans;
  int n = (int)s.size();
  for (char c = 'a'; c <= 'z'; c++) {
    int cntC = 0;
    int last = -1;
    int lastC = -1;
    bool good = 1;
    for (int i = 0; i < n; i++) {
      if (s[i] == c) lastC = i;
      if (s[i] < c) last = i;
      if (i - last == m) {
        if (lastC <= last) {
          good = 0;
          break;
        }
        cntC++;
        last = lastC;
      }
    }
    if (0) cerr << c << ' ' << cntC << endl;
    if (good) {
      for (int i = 0; i < cntC; i++) ans += c;
      break;
    }
    for (int i = 0; i < n; i++) {
      if (s[i] == c) ans += c;
    }
  }
  cout << ans;
  fprintf(stderr, "\nTIME = %lf\n", 1.0 * clock() / CLOCKS_PER_SEC);
  ;
  return 0;
}
