It's 4 stroke.
1st Stroke : Intake Fuel
2nd Stroke : Compress Fuel
3rd Stroke : Creates Energy (forgot exact word, but it's burning of fuel)
4th Stroke : Exhaust Gas.
The 2 stroke does 1 & 4 in 1st stroke and 3 & 4 in 2nd stroke.
EDIT : and also it's 2 piston account differently for strokes.