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;
using ll = long long int;
const int mod = 1000000007;
int main(int argc, char *argv[]) {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int m;
  string s;
  cin >> m >> s;
  vector<int> letters(26, 0);
  for (char c : s) {
    letters[c - 'a']++;
  }
  char mx = -1;
  int mxi = 0;
  int i = 0;
  while (i + m <= s.size()) {
    int j = i;
    int mn = -1;
    int mnj = -1;
    while (j < i + m) {
      if (s[j] < mx) {
        i = j;
        mnj = -1;
        mn = -1;
        break;
      }
      if (mn == -1 || s[j] <= mn) {
        mn = s[j];
        mnj = j;
      }
      j++;
    }
    if (mnj != -1) {
      if (mx < mn) {
        mx = mn;
        mxi = 1;
      } else if (mx == mn)
        mxi++;
      i = mnj;
    }
    i++;
  }
  char c = 'a';
  while (c < mx) {
    for (int i = 0; i < letters[c - 'a']; ++i) cout << c;
    c++;
  }
  for (int i = 0; i < mxi; ++i) cout << mx;
  return 0;
}
