How to create a new variable in sas? -

i want create new variable equal column sum of existing variable.the code using is-

data west; input total; set yash123;  total=sum monthly_sales; proc print data=west; var total; run; 

but not working.

a simple proc summary appear need :

 proc summary data=yash123 nway ;   var monthly_sales ;   output out=west (drop=_:) sum(monthly_sales)=total ; run ;