You would like to sort some monthly magazines in different categories.
Disregarding the title of magazines, there are 4 different categories if you arrange magazines by publishing year and month.
Disregarding the publishing year, there are 5 different categories if you sort magazines by title and month.
Disregarding month, you could divide magazines in to 6 different categories if you sort magazines by title and publishing year.
How many monthly magazines you have at most?
There is no magazine with the same title, publishing year and month. Each categorization does not need to have the same number of magazines.