I need minimum 3 Bitcoin to buy new computer. So, if I had a bitcoin I would wait for another 2 bitcoin.
Wouldn't it be wiser to invest those first and increase your money? Then use it to buy? 
The more bitcoin you invest, the more bitcoin you lose. Gimme one really safe way where to invest with near zero chance of losing it
Just Dice, maths pretty much means your investment can only go up in the long run. Approx 35% per annum at the moment is what you can expect.