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 N = 1e5 + 10;
const int inf = 1e9 + 10;
string s, d = "", f = "";
int m, n;
int a[N];
bool u[30][N];
char g = 'z';
map<char, int> mp, lp;
deque<int> dq, de;
int main() {
  cin >> m >> s;
  n = s.size();
  for (int i = 0; i < s.size(); i++)
    a[i + 1] = int(s[i] - 'a' + 1), lp[s[i]]++, g = min(g, s[i]);
  for (int i = 1; i <= m; i++) {
    while (!dq.empty() && dq.back() >= a[i]) dq.pop_back(), de.pop_back();
    dq.push_back(a[i]);
    de.push_back(i);
  }
  mp[char((dq.front() - 1) + 'a')]++;
  u[dq.front()][de.front()] = 1;
  for (int i = 2; i <= n - m + 1; i++) {
    if (dq.front() == a[i - 1] && de.front() == i - 1)
      dq.pop_front(), de.pop_front();
    while (!dq.empty() && dq.back() > a[i + m - 1])
      dq.pop_back(), de.pop_back();
    while (!dq.empty() && dq.back() == a[i + m - 1] && !u[dq.back()][de.back()])
      dq.pop_back(), de.pop_back();
    dq.push_back(a[i + m - 1]);
    de.push_back(i + m - 1);
    if (!u[dq.front()][de.front()]) {
      u[dq.front()][de.front()] = 1;
      mp[char((dq.front() - 1) + 'a')]++;
    }
  }
  sort(s.begin(), s.end());
  for (int i = 0; i < s.size(); i++) {
    if (mp[s[i]] > 0) f += s[i];
  }
  g = f[f.size() - 1];
  int i;
  for (int i = 0; i < s.size(); i++) {
    if (int(s[i]) < int(g))
      d += s[i];
    else {
      if (mp[s[i]] < lp[s[i]]) {
        lp[s[i]]--;
        continue;
      }
      d += s[i];
    }
  }
  cout << d << endl;
  return 0;
}
