IF THEN ELSE simple formula

Hello all,
I've written down some formulas to calcuation the effort on the following basis:

Total number of screens that could be tested in a CW - 220

Maximum Number of screens Per person per week - 20

Now, the logic goes this way :

For J3:
IF(A3=A2) THEN J3=J2 - I3.
Else J3 = (220-F3)/220


For J4:

IF(A4=A3) THEN J4= J3-I4
ELSE J4= (220-F4)/220

Similarly,
For J5:

IF(A5=A4) THEN J5= J4-I5
ELSE J5= (220-F4)/220

and so on...

Note :In the above mentioned formual, it should add up values in F only if, the values in A are identical.

So ideally, in J6 I should be getting the result as (90.91-2.73) i.e J5-I6.

Could you please suggest me the correct formula for this?