Where to pay exceeded stay days in Peru? (Lima)

Hi all,

I hope somebody can answer this question as soon as it gets ;).
I am leaving Peru next week and would like to know where do I have to pay the exceeded stay days in Peru (in Migraciones? at the airport when leaving?).
I know it costs $1 per day if a foreigner stayed after the Protected content permitted without any visa.

In addition to that, which are the documents to be presented before leaving Peru in such a case?.

I would really appreciate your answers.

Regards