As others have said you can get an air filter for your room and do your best to smoke-proof your door. But these will be stop-gap measures at best.
The smoke and yellow stains will gradually start bugging you until you will either have to move out or get angry with these folks and lose them as friends. The places a person can smoke with impunity these days are fewer and fewer, and their apartment may be close to the last place where they are free to indulge. The new guy, and the one in the minority, simply has no right to move in and then try to change the rules.
If you don’t smoke and you choose to live with smokers you might as well take up smoking yourself. You wouldn’t notice their smoke any longer or the smell on your clothes and possessions. The drawback, of course, is that cigarettes are really expensive, and of course there is that whole COPD thing.
My husband used to be a smoker. He quit almost twenty years ago so his lungs should be back to equal to a non-smoker’s lungs, right? Not so. He has COPD from the years he did smoke and it isn’t going away. In fact, as he ages it is only getting worse.
My suggestion is to tell your friends thanks but no, thanks. That way you can keep them as friends.