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

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

Example Input: All imaginary numbers are complex numbers with _ for the real part.
Example Output: zero

Example Input: Horses do have _ blind spots, however.
Example Output:
two