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I begun with $110... you never know.
So far everything is going fine so i added another 220$.
If in a month everything keeps going good i will invest more.

If you are starting out start with as much as you are willing to see disappear. For me that was 2.5 TH/s or $550 USD. If you have $1100 USD I would suggest that as you would get 5 TH/s giving you a good starting point but again start with something you don't mind loosing tomorrow.