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

Input: Consider Input: Stroke is our nation's number _ killer, and a leading cause of disability for older adults.

Output: three

Input: Consider Input: All children normally wake up four or _ times each night after dreams.

Output: five

Input: Consider Input: Most mammals have _ cervical vertebrae, but sloths possess nine.
Output: seven