In a bowl mix the sugar and yoghurt. In 100 ml pineapple juice dissolve both gelatin and rotate for 20 seconds in the microwave. Add to milk. In 4 cups put some of the pieces of pineapple and a few cherries. Spread top milk mixture. Wait just set and arrange on top the rest of the pineapple fruit and again a few cherries. With a spoon carefully pour part of syrup of cherries, to form a thin red layer (at first not waited and mingled in the second to arrive) and put in the fridge to cool.