Given a string of lowercase English letters and an integer of the substring length, determine the substring of that length that contains the most vowels. Vowels are in the set $\{a,e,i,o,u\}.$ If there is more than one substring with the maximum number of vowels, return the one that starts at the lowest index. If there are no vowels in the input string, return the string $\text{'}$ Not found!$\text{'}$ without quotes.

Example $1$

$s=$ 'caberqiitefg'

$k=5$

The substring of length $k=5$ that contains the maximum number of vowels is 'erqii' with $3$ vowels. The final answer is 'erqii'.

Example $2$

$s=$ 'aeiouia'

$k=3$