In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.

Example Input: Puppies can start vaccinations at _ weeks.
Example Output: six

Example Input: Young groundhogs are weaned and ready to seek their own dens at _ to six weeks of age.
Example Output: five

Example Input: Infertility is fairly common, and about one out of every _ couples is infertile at any given time.
Example Output:
six