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 m;
string s;
int hs[300000];
int tail, frt;
int main() {
  cin >> m;
  cin >> s;
  char c = 'a';
  m--;
  for (; c <= 'z'; ++c) {
    deque<int> Q;
    int i = 0;
    int j = 0;
    bool flag = true;
    Q.push_back(0);
    while (i < s.size() && j < s.size()) {
      while (j < s.size() && (j - i) < m) {
        ++j;
        while (!Q.empty() && s[Q.front()] >= s[j]) Q.pop_front();
        Q.push_front(j);
      }
      if (j >= s.size()) break;
      if ((j - i) == m) {
        while (!Q.empty() && Q.back() < i) Q.pop_back();
        if (s[Q.back()] > c) flag = false;
      }
      ++i;
    }
    if (flag) break;
  }
  vector<char> ans;
  for (int i = 0; i < s.size(); ++i) {
    if (s[i] < c) ans.push_back(s[i]);
  }
  {
    deque<int> Q;
    int i = 0;
    int j = 0;
    bool flag = false;
    Q.push_back(0);
    int last = -1;
    if (s[0] == c) last = 0;
    while (i < s.size() && j < s.size()) {
      while (j < s.size() && (j - i) < m) {
        ++j;
        while (!Q.empty() && s[Q.front()] >= s[j]) Q.pop_front();
        Q.push_front(j);
        if (s[j] == c) last = j;
      }
      if (j >= s.size()) break;
      if ((j - i) == m) {
        while (!Q.empty() && Q.back() < i) Q.pop_back();
        if (s[Q.back()] == c && flag == false) {
          hs[last] = 1;
          ans.push_back(c);
          flag = true;
        }
      }
      if (hs[i] == 1) flag = false;
      ++i;
    }
    sort(ans.begin(), ans.end());
    for (int i = 0; i < ans.size(); ++i) cout << ans[i];
    cout << endl;
  }
  return 0;
}
