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

Input: Consider Input: Natural iron contains _ isotopes and isomers.

Output: four


Input: Consider Input: Special relativity shows that time behaves surprisingly like the _ spatial dimensions.

Output: three


Input: Consider Input: Crustaceans are the only arthropods that have a. b. c. d. _ pairs of legs.


Output: three