Spanish citizens (and most of latin-american) officially have two surnames. Your first surname is your father's first and your second is your mother's first. Women do not change their name when they marry. This seems to imply women's equality with respect to names, but it does not. You use your two grandfathers' surnames and forget your two grandmothers'. (Of course, the law allows parents to switch the surnames of their newborns when inscribing them, but most people don't do it).
Unofficially, the sequence of surnames is infinite. You have your father's second surname as your third, your mother's second as your fourth, your father's third as your fifth, and so on. My sequence up to the sixteenth term is Santos Leal Corchero Villalba Herrera Ramos Ponciano Rebollo Martín Vallecillo Gallardo Guillén Suárez Cabezón Pavo Fernández.
A more balanced choice would have been to take as your odd-indexed surnames those of the parent of your same sex. But then, how does the infinite sequence behave? Answer: for each power of 2, your first 2^i surnames are the first surname of your 2^i ancestors in the i-th generation, ordered according to the following self-similar sequence of sexes (a is your sex and b is the opposite one):
i=1: ab
i=2: abba
i=3: abbabaab
i=4: abbabaabbaababba
i=5: abbabaabbaababbabaababbaabbabaab
i=6: abbabaabbaababbabaababbaabbabaabbaababbaabbabaababbabaabbaababba
In case you did not notice, the first half in each row equals both the odd part of that row and the previous row. The first and second halves of a row are opposite to one another, as are the odd and even parts. Even rows are symmetric under middle reflection and odd rows are antisymmetric. The infinite sequence obtained is known by combinatorialists as the Thue-Morse sequence.
By the way, Leal means loyal. And you already know what Santos means, don't you?.