Multiple logical test - excel problem help please

Hi, i am stuck in the formula.
A = TARGET COMPLETION DATE (example 15/09/2015)
B = ACTUAL COMPLETION DATE (example 14/09/2015)
C = STATUS (MEET SCHEDULE OR BEHIND SCHEDULE)
D = A cell which able to show ICON SETS base on data from C. If Meet Schedule, show a Green Circle. If Behind Schedule, show a Red Circle.

I want to create a formula to justify C.
Condition as following:

if A or B is blank, then C = blank.
But:
if B<=A, then C = MEET SCHEDULE
if B>A, then C = BEHIND SCHEDULE

Please help.....

THANKS. Any idea on the Red and green icon?