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

Example Input: Conserved residues make similar contacts in _ repressor-operator complexes.
Example Output: two

Example Input: Metals often crystallize in a _ dimensional version of the hexagonal closest packed structure.
Example Output: three

Example Input: Harvesting occurs every _ to four years in the winter after leaves fall from the trees.
Example Output:
three