Hi Kabayan! 

You shouldn't think of how much exactly you invest, but rather what percentage of your funds you're going to invest into bitcoins. Before investing yourself, I suggest reading articles and watch videos about Bitcoin and cryptocurrency so you know what you're investing on. Don't invest just because some people invest. Learn about crypto and make your own judgement.

After learning about bitcoin, ask yourself. Do you believe bitcoin will be successful? If yes, how likely? And then think of how much of your total money you should invest. DON'T invest more than you are willing to lose. You wouldn't want to be homeless if ever bitcoin goes to sh*t.