Answer:
I have a doubt because I think that once the result of the first coin is obtained, just simply await the outcome of the second, which is completely independent of the previous one, and then we have a chance of 1/2 to get a head again.
But someone else tells me that as the possible events are:
Head - Head
Head - Tail
Tail - Head
Tail - Tail
then when we get a head we restrict ourselves to the first three cases, so the probability would be 1/3
