HMMT 2013 U36

(Mathematicians A to Z) Below are the names of 26 mathematicians, one for each letter of the alphabet. Your answer to this question should be a subset of $\{A, B, \cdots, Z\}$, where each letter represents the corresponding mathematician. If two mathematicians in your subset have birthdates that are within 20 years of each other, then your score is 0 . Otherwise, your score is $\max (3(k-3), 0)$ where $k$ is the number of elements in your subset.