That's a very easy question to answer, zip, none, nadda, run run as fast as you can ... away from them. Don't even go that way. There is tons of information out there everywhere to tell and show you why none is the answer. Check it out.
I smoked for a long time. I am paying a steep price for that. Cancer, COPD, surgeries, chemotherapy, etc, etc, etc, etc, etc. If you smoke, quit. If you don't smoke, don't start. There is absolutely no safe level of smoking!
The problem is that they are habit forming. If you get hooked you won't be able to stop at a number. I never got hooked so will occasionally have one with a particular friend. Key for me is never buying them.
My mother, a smoker, died of lung cancer at 68. I smoked 25 yrs, but quit 23 yrs ago, and I now have asthma, and often have pneumonia. Thank goodness I quit when I did. My daughter is 46, has chronic bronchitis, wiping her out 3 or 4 times a year. My 25 yrs old granddaughter smokes. You may start off thinking you can handle it - and it is good with that first cup of coffee (or that first beer), but you NEVER KNOW when you cross the line and NEED a cigarette to calm down. You're hooked. Quit NOW. Completely! That's your best bet. After 5-7 years of not smoking, your lungs will ALMOST return to normal, if they're not too damaged already.
There is no safe number of cigarettes. If you REALLY want to quit, look into hypnosis. It works. Better than patches or gum and waaay more successful than trying to quit cold turkey. Go on-line and find a good hypnotherapist in your area and have a chat. It's never too soon to quit.
Your lungs are designed to provide healthy nutrients and oxygen-rich blood to very important parts of your body. Not sure why anyone would want to inhale toxic materials, yes toxic materials into their lungs.
Please don't smoke, there really isn't any healthy benefit from it. Plus, you'll save yourself between $1,500-$2,000 a year. Think of all the things you could buy with those savings.