How to create a formula based on if function

[LL19911695]

I am trying to create a formula that is essentially (based on dummy data below):

(in cell c2) - if A2 is equal to A3, subtract b3 from b2. 

Is this even possible?!

1	A	B	C
2	Joe Bloggs	100
3	Joe Bloggs	95
4	John Doe	300
5	John Doe	200
6	John Doe	200

[#2]

@LL19911695 

In C2:

=IF(A2=A3,B2-B3,"")

Fill down.