I want to use Mathematica to solve the problem:
Find the maximum $k$ such that $6x+9y+20z=k$ does not have a non-negative solution.
I tried FrobeniusSolve. But what is the elegant way to find the maximum?
I know the theoretical background of this problem, and I know other ways of getting the solution. But I want to see how this can be done elegantly in a program in Mathematica.