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 $1 ≤ *i*_{1} < *i*_{2} < ... < *i*_{*t*} ≤ |*s*|$. 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 $*s*_{*i*_{*p*_{1}}}*s*_{*i*_{*p*_{2}}}... *s*_{*i*_{*p*_{*t*}}}$.

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.

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".