Excel Formula Needed Please

I made an example sheet:
\1

I have a list of over 1000 "Cusip" Numbers that have a price and a price source for about 60 days. The prices for the Cusips may change every day, and the source of the price may change as well. I'm looking for a formula that will spit out how often each Cusip changes sources.

In the example above:
Cusip 1 uses the same source for all four days -> 0 switches
Cusip 2 changes from source A to B on the 1/2/99 and stays with source B from then on -> 1 switch
Cusip 3 changes from A to B and then from B to A -> 2 switches
Cusip 4 changes from A to C, from C to B, and from B to A -> 3 switches

Thanks!