The first stage is to describe the problem in natural language.

What is the unknown information--the decision variables--in this problem?

What are the values of x and y?

What are the limits or restrictions on combinations of these values--the constraints--in this problem?

Though the Describe stage of the process may seem trivial in a simple problem like this one, you will find that taking the time to fully describe a more complex problem is vital for creating a successful program. You will be able to code your program more quickly and effectively if you take the time to describe the model, isolating the decision variables and constraints.