The Four progression falls into two 16 bar sections which add up to 32 bars in total. The first twelve bars of these two sections are identical, with the last four bars taking different paths through the harmony to lead back to the progression's beginning.
	You could call the first 16 bars the A section and the second 16 bars, the A' (A prime)section since the last 16 is the A section with a diferent tail attached starting in the 12th bar for variation's sake.