Three vessels; the largest starts full, the others empty. There is no tap and no drain — the only move is to pour one vessel into another, which transfers liquid until the source is empty or the destination is full. Tap a vessel to pick it up, then tap another to pour (tap it again to put it down). Read the tick marks: every line is one cup. Finish with exactly the target amount in any vessel. Keys: 1/2/3 select and pour, U undo, R restart.