Excel 2008 : i need formula for cumulative frequency for two coexisting values in two different columns

i want help with ms excell 2010

i have two columns and i want formula that will add up the frequency of value in both columns whenever they are same, e.g

a	b	1
c	d	1
a	b	2
b	a	1
a	b	3

i want formula that will do this for me every time same value occurs in the two colums