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

Input: Consider Input: All imaginary numbers are complex numbers with _ for the real part.

Output: zero


Input: Consider Input: Equations are statements which say that _ quantities are equal.

Output: two


Input: Consider Input: Brook stickleback have prominent mouths, large eyes and _ to six spines on their backs.


Output: four