its all about the bullets

there is an alien invasion and you need to stop them! you have a line of cannons that... shoot. each ship of the aliens can be hit from up or down. you need to flip the cannons in order to stop them from passing you and reaching into the base. you got three lives before its a game over. how do you win? you dont, its an infinite game. controls: 1 2 3 4 5 6 to shoot with the cannons (A) to flip the cannons down (S) to flip them up