EOJ-自适应编程学习平台

Tim is an absolutely obsessive soda drinker,he simply cannot get enough. Most annoyingly

though, he almost never has any money, so his only obvious legal way to obtain more soda is to take the money he gets when he recycles empty soda bottles to buy new ones. In addition to the empty bottles resulting from his own consumption he sometimes find empty bottles in the street. One day he was extra thirsty, so he actually drank sodas until he couldn't aford a new one.

Three non-negative integers $e,f, c$, where $e < 1000$ equals the number of empty soda

bottles in Tim's possession at the start of the day, $f < 1000$ the number of empty soda

bottles found during the day, and $1 < c < 2000$ the number of empty bottles required to

buy a new soda.

How many sodas did Tim drink on his extra thirsty day?