Even numbers

Slide the tiles in one of four directions, if meet two tiles with the same number on them, they turn into one to 2 times more. With each turn, new tiles with small numbers. First, the game seems very simple, while the tiles is small, the number is small, lots of space. But when the largest tile size be 128, 256, 512, then the field becomes not so free and you need to think about each move. After all, if the field is filled, the game is over, undo moves, no.