The series combination of the three 12uF capacitors is 12uF/3 = 4uF.
Now you have 4uF in parallel with 4uF on the bottom leg that gives 8uF.
8uF in series with the 8uF capacitor on the top leg gives 4uF.
Finally, 4uF in parallel with the input 4uF capacitor gives 8uF.
The input CIN is therefore 8uF.