Nobody can tell you when you are least likely to get pregnant in terms of days. This is because, even if you have a very regular menstrual cycle, the timing of ovulation can vary a lot from cycle to cycle (and everyone's cycle is different).
The time you are most likely to get pregnant is around ovulation - specifically, in the five days before it and two days after it (since sperm can survive in the body for up to five days - and in a few cases, have been known to survive for longer).
But unless you have a very regular cycle and are practising the "fertility awareness method" (which includes taking your basal body temperature every day and monitoring your cervical mucus), it's impossible to predict with any accuracy when you are ovulating. And trying to guess is not a good idea.
So your best bet is to make sure that you are using an effective method of contraception. I recommend that you check out Scarleteen's article on birth control at http://www.scarleteen.com/reproduction/birthcontrol.html , which gives information on different forms of contraception.
If you're using an effective method of contraception and practising safer sex - for example, taking the pill and using condoms - then the timing in your cycle is not going to make a significant difference.