Your objective is shoot in balls with even or odd numbers.
During the game, background change between even and odd. When you shoot in the correct ball, the number in ball is added your score. when you wrong, you lose the number in ball x 2.
When you shoot in correct balls in a row, your multiplier is increased. The multiplier multiplies the number of next correct ball you shoot. Each time that your multiplier is a multiple of ten, you gain a heart.