main(_) ->
        L=a(date(),{2013,12,31}),
    M=[{X,Y,13} || {X,Y,13} <- L, calendar:day_of_the_week({X,Y,13}) =:= 5],
    io:format("~p~n~p days~n", [M, length(M)]).

a(X,X) -> [X];
a(X,Y) -> [X] ++ a(calendar:gregorian_days_to_date(
                 calendar:date_to_gregorian_days(X)+1),Y).