Umm, there's really no way for us to answer this. Start out with a small line or two, and see how you feel, and go from there. There is a super compulsion to redose with this stuff, and you may find that it's incredibly overrated for how expensive it is. I'd say a half gram would be a good starting amount, but this is also to be done throughout the evening, not all at once. It's just that sort of drug. Take it slow, see how you feel...and, none of us have any idea of the quality of the coke you have, it could be so good that a little bump gets you feeling awesome, or so shitty that a few lines seem to have very little effect.