# Soda Surplier

Tim is an 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 finds empty bottles in the street. One day he was extra thirsty, so he drank sodas until he couldn't afford a new one.

## Input

Three non-negative integers $e,f,c$, where $e(e<1000)$ is the number of empty soda bottles in Tim's possession at the start of the day, $f(f<1000)$ is the number of empty soda bottles found during the day, and $c(1<c<2000)$ is the number of empty bottles required to buy a new soda.

## Output

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