Print the report, specify the total number of observations in each BY group, and suppress the printing of observation numbers. N= prints the number of observations in a BY group at the end of that BY group. The explanatory text that the N= option provides precedes the number. NOOBS suppresses the printing of observation numbers at the beginning of the rows. LABEL uses variables' labels as column headings.

proc print data=exprev n='Number of observations for the month: ' 
           noobs label;