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;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
set<pair<int, char> > sa;
string alpha = "abcdefghijklmnopqrstuvwxyz";
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int m;
  string s;
  cin >> m >> s;
  sa.insert({-1, '$'});
  sa.insert({int(s.size()), '$'});
  for (int t = 0; t < 26; t++) {
    for (int i = 0; i < s.size(); i++)
      if ((s[i] - 'a') == t) sa.insert({i, alpha[t]});
    bool isvalid = 1;
    for (auto it = sa.begin(); it != sa.end(); it++) {
      if (it == sa.begin()) continue;
      auto it2 = it;
      it2--;
      pair<int, char> p = *it;
      pair<int, char> q = *it2;
      if ((p.first - q.first) >= (m + 1)) isvalid = 0;
      if (!isvalid) break;
    }
    if (isvalid) {
      for (auto it = sa.begin(); it != sa.end(); it++) {
        pair<int, char> p = *it;
        if (p.second == alpha[t]) {
          auto it2 = it, it3 = it;
          it2--;
          it3++;
          pair<int, char> q = *it2;
          pair<int, char> r = *it3;
          if ((r.first - q.first) < (m + 1)) {
            sa.erase(it);
            it = it2;
          }
        }
      }
      break;
    }
  }
  string ans = "";
  for (auto it = sa.begin(); it != sa.end(); it++) {
    pair<int, char> p = *it;
    if (p.second != '$') ans += p.second;
  }
  sort(ans.begin(), ans.end());
  cout << ans << endl;
  return 0;
}
