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, s = input(), raw_input()
id = [-1] * 26
for i in range(m):
  id[ord(s[i]) - ord('a')] = i
pos, res, vis = -1, '', [0] * 10**5
for i in range(26):
  if id[i] >= 0:
    pos, res, vis[id[i]] = id[i], res + chr(ord('a') + i), 1
    break
for i in range(m, len(s)):
  id[ord(s[i]) - ord('a')] = i
  if pos < i - m + 1:
    for j in range(26):
      if id[j] >= i - m + 1:
        pos, res, vis[id[j]] = id[j], res + chr(ord('a') + j), 1
        break
res = ''.join(sorted(res))
c = res[-1]
for i in range(len(s)):
  if vis[i]: 
    continue
  if s[i] < c:
    res += s[i]
print ''.join(sorted(res))
    