TSA 2021 · Question 24 · Optimisation
SaveA cinema uses magnetic letters to write the title of the most popular film that it is screening on its advertisement board. A set of magnetic letters includes the letters of the English alphabet in both upper and lower cases, i.e. 26 capital letters and 26 small letters. The cinema has just enough sets to be able to write the following title:

What is the minimum number of extra sets of magnetic letters that the cinema needs to buy?