A catering company must meet its daily demand for clean napkins by either buying new napkins, using regular laundry service which requires a full day turnaround, or special overnight service. Supplied with the demand for each of the next $5$ days, and the costs for new napkins, regular laundry service, and overnight laundry service you have been asked to develop a model which will minimize the cost of procuring the napkins over the next $5$ days. The company currently has no napkins in usable condition, clean or dirty, on the premises or at the laundry. Formulate this problem as a Minimum Cost Network Flow model.