Man, I was kinda daydreaming on maybe getting A for free yesterday. On average, I need to spend about 200 stamina points to get 4 to 5 points. That means roughly 200000 stamina points minimum. Take away 7 days of 350 stamina points, that leaves 197550 stamina points, or 19755 bottles of stamina potions minimum.

But alas, stamina potions are not purchasable with coupons, despite myself clearly remembering that the shop usually do sell them. I suspect the game purposely took them out to prevent anyone from being able to possibly grind A out for free.