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".
m = int(input())
s = input().strip()

sa = [0] * len(s)
for i in range(len(s)):
	sa[i] = ord(s[i]) - ord('a')

sa = [-1] + sa + [-1]

def check_value(sa, m, threshold):
	prev_ind = 0
	for i in range(len(sa)):
		if sa[i] <= threshold:
			if i - prev_ind <= m:
				prev_ind = i
			else:
				return False
	return True

def get_indexes(sa, threshold):
	seq = [i for i in range(len(sa)) if sa[i] <= threshold]
	# seq = []
	# for i in range(len(sa)):
	# 	if sa[i] < threshold:
	# 		seq[i].append(sa[i], i)
	return seq

def filter_indexes(sa, seq, el, m):
	new_seq = [0]
	for i in range(1, len(seq) - 1):
		if sa[seq[i]] != el or (sa[seq[i]] == el and seq[i+1] - new_seq[-1] > m):
			new_seq.append(seq[i])
	return new_seq[1:]


threshold = -1
while (not check_value(sa, m, threshold)):
	# print(threshold, get_indexes(sa, threshold))
	threshold += 1
# print(threshold, get_indexes(sa, threshold), sa)

seq = get_indexes(sa, threshold)
seq = filter_indexes(sa, seq, threshold, m)

s = ''.join(sorted([chr(ord('a') + sa[x]) for x in seq]))
print(s)