Preheat oven to 350°. Before draining pineapple, remove and reserve 3 tablespoons of the juice. Mix juice with flour and sugar. Add pineapple and cheese. Put in greased 8- or 9-inch casserole. Mix butter and Ritz crumbs. Sprinkle on top of casserole. Bake for 20 to 30 minutes. Recipe may be doubled and baked in 9 x 13-inch pan.