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

Example Input: Lightning can travel _ miles or more horizontally from the storm, then strike the ground.
Example Output: six

Example Input: Ice jams cause flooding because of _ main features.
Example Output: two

Example Input: Antibodies exist as one or more copies of a Y-shaped unit, composed of _ polypeptide chains.
Example Output:
four