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

Example Input: Pelycosaurs are a paraphyletic group of _ primitive families of synapsids.
Example Output: six

Example Input: Cigarette smokers have up to a _ times higher incidence of bladder cancer than non-smokers.
Example Output: four

Example Input: Most people remove ashes every _ to three weeks.
Example Output:
two