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 long nmax = 1e5 + 3;
deque<long> dq;
string s;
long m, c[nmax], a[28];
long cc(char x) { return (int(x) - int('a')); }
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> m;
  cin >> s;
  char mx = 'a';
  long i, j;
  i = 0;
  while (i + m - 1 < s.length()) {
    long t = i;
    for (j = i + 1; j < i + m; j++)
      if (s[j] <= s[t]) t = j;
    c[t] = 1;
    mx = max(mx, s[t]);
    a[cc(s[t])] += 1;
    i = t + 1;
  }
  for (i = 0; i < s.length(); i++)
    if (s[i] < mx && c[i] == 0) a[cc(s[i])] += 1;
  for (char ch = 'a'; ch <= 'z'; ch++)
    for (i = 1; i <= a[cc(ch)]; i++) cout << ch;
}
