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".
from collections import defaultdict

class DenseSubsequence():
    def __init__(self, m, s):
        self.m = m
        self.s = s
        self.chars = sorted(set(s))

    def get_min_sequence(self, ch, mask):
        lv, lch, i = -1, -1, 0
        is_possible = True
        seq = []
        while i < len(self.s):
            if mask[i] == 1:
                lv = i
            elif self.s[i] == ch:
                lch = i

            if i-lv == self.m:
                if lch > lv:
                    seq.append(lch)
                    lv = lch
                else:
                    is_possible = False
                    break
            i += 1
        if not is_possible:
            return False, []
        else:
            return True, seq

    def get_sequence(self):
        char_map = defaultdict(list)
        for i in range(len(self.s)):
            char_map[self.s[i]].append(i)

        mask = [0]*len(self.s)

        res = ''

        for ch in self.chars:
            is_possible, seq = self.get_min_sequence(ch, mask)
            if is_possible:
                res = res+''.join([ch]*len(seq))
                break
            else:
                res = res+''.join([ch]*len(char_map[ch]))
                for v in char_map[ch]:
                    mask[v] = 1
        print(res)

m = int(input())
s = input().strip(' ')
DenseSubsequence(m,s).get_sequence()