How can it be safe if it's not safe?

Female safety period usually refers to the low probability of pregnancy period, if the female menstrual cycle is regular, the whole cycle is 28 days, first excluding menstrual period 7 days, followed by excluding ovulation period 7 days, and ovulation period 14 days before the next menstrual period, then the female menstrual period one week before and one week after the end of the safe period.