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D. Dense Subsequence

time limit per test

2 secondsmemory limit per test

256 megabytesinput

standard inputoutput

standard outputYou 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 ≤ *i*_{1} < *i*_{2} < ... < *i*_{t} ≤ |*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* ≤ *i*_{k} ≤ *j* + *m* - 1.

Then we take any permutation *p* of the selected indices and form a new string *s*_{ip1}*s*_{ip2}... *s*_{ipt}.

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".

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