1. Buy 10 ---- If you lose money, you should buy 30 rupees
2. Buy 30 --- If you lose money, you should buy 90 rupees
3. Buy 90 --- If you lose money, you should buy 270 rupees
If you win, you can make 270--90-30-10 = 140
Buy 270 rupees, if you lose - you should buy 810 rupees
If you win, you can make 810-270--90-30-10 = 410
