how to count observations and put them in groups

wondering if this was possible. i have a database that has identifies all the tires on many different vehicles (from cars to 18 wheelers). im trying to figure out how many vehicles there are in the data set. the easiest way (it seems to me), is to tell sas to add 1 to a variable whenever then make of the vehicle changes. the list of observations looks like this. As you can see, the vehicles have different numbers of tires, which makes it tough to count them.
VOLVO
VOLVO
VOLVO
VOLVO
VOLVO
VOLVO
INTERNATIONAL
INTERNATIONAL
INTERNATIONAL
INTERNATIONAL
INTERNATIONAL
INTERNATIONAL
KENWORTH
KENWORTH
KENWORTH
KENWORTH
KENWORTH
KENWORTH
KENWORTH
KENWORTH
KENWORTH
KENWORTH
TRAILMOBILE
TRAILMOBILE
TRAILMOBILE
TRAILMOBILE
TRAILMOBILE
TRAILMOBILE
TRAILMOBILE
TRAILMOBILE
UTILITY
UTILITY
UTILITY
UTILITY
UTILITY
UTILITY
UTILITY
UTILITY

any help would be appreciated