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".
#!/usr/bin/env python
# coding: utf-8

if __name__ == '__main__':
    from collections import Counter
    from string import ascii_lowercase as asc

    import sys
    f = sys.stdin
    #f = open('/home/ilya/opt/programming/tasks/724D.txt')

    if False:
        import io
        f = io.StringIO("""3
bcabcbaccba""")
        
    if False:
        import io
        f = io.StringIO("""2
abcab""")
        
    if False:
        import io
        f = io.StringIO("""5
wjjdqawypvtgrncmqvcsergermprauyevcegjtcrrblkwiugrcjfpjyxngyryxntauxlouvwgjzpsuxyxvhavgezwtuzknetdibv""")
        
    if False:
        import io
        f = io.StringIO("""5
addcdbddddbddddcc""")

    if False:
        import io
        f = io.StringIO("""1
addcdbddddbddddcc""")

    def read_int_line():
        return list(map(int, next(f).split()))
    
    def getline():
        return next(f).rstrip('\n\r')

    m = read_int_line()[0]
    s = getline()
    
    g = Counter(s)
    
    def solve(c):
        p = 0
        for q in ''.join(x if x >= c else ' ' for x in s).split():
            i, j = 0, -1 
            while j + m < len(q):
                j = q.rfind(c, j + 1, j + m + 1)
                if j == -1:
                    return None
                i += 1
            p += i
        return p
    
    for c in asc:
        f = solve(c)
        if f is not None:
            g[c] = f
            print(''.join(x*g[x] for x in asc if x <= c))
            break