I just found out im prego but I smoke ciggerrette , I'm 5 wks prego?

I have normally about 5 to 7 cig.s A day but last week I tried going cold turkey and I did pretty good until I had a stressful day at work/home , so I ended up having 5 through out the whole week..... I feel so guilty !!! What's the least amount I could have & when is the best time to quite before it really effects my baby???