When is my safiest day to have safe sex if i took birth control pills for 4 days and then i stop using it?

there is no safe days if you only took it for four days, its only effective from the first day of your period if you take it consistently, if you start during the month then you need to be on it for a month before its fully effective,

only 4 days taking it is not going to stop you getting pregnant.

its not worth the risk, start taking it again or use a condom.