Given integers a,b,c such that gcd(a,b,c) = 1 it is well known that there exists only a finite set of numbers b such that b is not expressible as ax+by+cz for non negative integers x,y,z.

It is also known that there exists a quadratic time algorithm for finding the maximal such b. However I was not able to spot the paper covering the algorithm.

Anybody happens to know the algorithm and/or a (free) reference to it?