TOFFIES IN JAR

There is a JAR full of toffies for sale at a mall counter. JAR has the capacity $N$, that is JAR can contain maximum $N$ toffies when JAR is full. At any point of time. JAR can have $M$ number of Candies where $M<=N$. toffies are served to the customers. JAR never remains empty as when last $k$ toffies are left. JAR is refilled with new candies in such a way that JAR gets full. Write a code t