A butcher shop is buying meat slicers for their shop, a manual and automatic slicer. The manual slicer can cut 5 slices per minute while the automatic slicer can cut 8 slices per minute. In addition, to make sure all the parts operate smoothly, the manual slicer requires 3 units of grease per minute while the automatic slicer requires 6 units of grease per minute. Since the automatic slicer does not need someone to operate it, the number of manual slicers must be less than the number of automatic slicers. In addition, the butcher shop needs to be able to cut at least 50 slices per minute but can use at most 35 units of grease per minute. How many of each slicer should the butcher shop buy to minimize the total number of slicers in the shop?