Alex had written all the $$$26$$$ letters from $$$a$$$ to $$$z$$$ on a board initially. Later, he rearranged those letters forming a new sequence. Alex gives you this new sequence of $$$26$$$ letters, another string $$$s$$$ of length $$$n$$$ and a number $$$k$$$.

Your task is to find and return the lexicographically smallest subsequence of length $$$k$$$ formed from string $$$s$$$, in accordance with the new sequence of letters provided to you.

Note: A subsequence of a string is formed by deleting a few (possibly $$$0$$$) characters from string. Given two strings, a string will be lexicographically smaller than other string, if it comes first in the dictionary.