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".
def inputarr(f = int, splitkey = ' '):
    return map(f, raw_input().split(splitkey))
m, = inputarr()
s = raw_input()
lens = len(s)
def check(a):
    bef = -1
    for i in a:
        #print i, bef
        if i - bef > m:
            return False
        else:
            bef = i
    return lens - 1 - bef < m

stlist = list(s)
d = dict()
for i, ch in enumerate(s):
    for key in range(ord(ch), ord("z") + 1):
        chkey = chr(key)
        d.setdefault(chkey,list()).append(i)

for key in range(ord("a"), ord("z") + 1):
    chkey = chr(key)
    #print chkey
    dlist = d.get(chkey,[])
    if check(dlist):
        bef = -1
        ans = []
        lend = len(dlist)
        lens = len(s)
        for i, j in enumerate(dlist):
            if stlist[j] != chkey \
                     or (i + 1 < lend and dlist[i + 1] - bef > m)\
                     or (i + 1 == lend and lens - bef > m):
                #print stlist[j] != chkey, i + 1 < lend and dlist[i + 1] - bef > m, i + 1 == lend and bef < lend
                ans.append(stlist[j])
                #print ans
                bef = j
        print "".join(sorted(ans))
        break
    else:
        pass