Everyone starts with a $5 safe!
Invest $5 and get back $7.5 in 3 days, which is 50% of the profit.
Now the investment safe opens for $10. After 5 days, you will receive $15.5 which is 55% of the profit.
(at the same time, you can invest in the $5 Safe again)
Then the investment safe opens for $25. After 7 days, you will receive $40, which is 60% of the profit.
So on and so forth till you get to the $2000 case.