P1215 [USACO1.4] Mother's Milk

Farmer John has three milking buckets of capacity $A$, $B$, and $C$ liters. Each of the numbers $A$, $B$, and $C$ is an integer from $1$ through $20$, inclusive. Initially, buckets $A$ and $B$ are empty while bucket $C$ is full of milk. Sometimes, Farmer John pours milk from one bucket to another until the second bucket is filled or the first bucket is empty. Once begun, a pour must be completed. Being thrifty, no milk may be tossed out. Write a program to help Farmer John determine what amounts of milk he can leave in bucket $C$ when he begins with three buckets as above, pours milk among the buckets for a while, and then notes that bucket $A$ is empty.

A single line with the three integers $A$, $B$, and $C$.

A single line with a sorted list of all the possible amounts of milk that can be in bucket $C$ when bucket $A$ is empty.

USACO Training Section 1.4.