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

Ex Input:
Vitamins are classified into _ groups.

Ex Output:
two


Ex Input:
Thermal equilibrium occurs when _ bodies have the same temperature.

Ex Output:
two


Ex Input:
Refraction occurs _ times, as the light intersects the vessel s inner and outer surfaces .

Ex Output:

four