You run a department store, and you are trying to schedule employees to cover shifts over the holiday various periods (Christmas, Thanksgiving, Independence Day, and so forth) for the coming year. For each employee, you have a list of what days they are available to work. Your goal is to assign employees to days so as to cover as many holidays as possible (hopefully all of them), subject to the following constraints: first, each employee can be assigned to at most c days in total so as not to be overworked. In addition, for each holiday period, each employee can be assigned to at most one day in that period. So, for example, you could assign an employee to work on one day during the Christmas holiday and one day on the Thanksgiving holiday, but not two days during the Christmas holiday. Show how to solve this as a network flow problem.