Ok, lots of ways to get that value.
What are you planning to do with it? Depending on what the next step is you may want it in a macro variable or data set. If you're looking for verification or to check it, that information is also in the log after the creation.
proc means data=have N;
run;
You can also use PROC CONTENTS to view a description of the data set:
proc contents data=have;
run;