Editorial for CCC '15 S2 - Jerseys
Submitting an official solution before solving the problem yourself is a bannable offence.
A simple greedy algorithm goes like this:
If a jersey is available for a person, give it to him immediately.
This works because we just want to maximize the number of people with jerseys, and each jersey given counts.
You can make the implementation easier by converting the sizes to integers ( for small, for medium, for large, and for taken).