一瓶啤酒售價$2，兩個空瓶換一瓶，四個瓶蓋\送一瓶。$10共可以喝幾瓶?
beer $2 each

A bottle of beer costs $2.
Two empty bottles: get one bottle for free
Four bottle caps : get one bottle for free
How many bottles can you have if you have $10?

2 empty bottles:
	get 1 bottle free
4 crown caps:
	get 1 bottle free

I have $10
beer	bottle	cap
5	5b	5c

total = ...
while(尚有酒送 free bottles){
	nfree = ...		// 送nfree瓶
	cap = ...		// 尚餘瓶蓋
	bot = ...		// 尚餘空瓶
	total = ...		// 目前共喝了total瓶
}
total no.of bottles 共喝了??瓶