How do I sum values from prevs value

[hk2013]

im trying to sum the previous number

intial total number is Num_1 + num_2 and than after its Num_2+total 

Have: 

date    num_1 Num_2 

06JAN2019  5  10   
13JAN2019  5  10   
20JAN2019 5   10  
27JAN2019  5  10  

want 

date    num_1 Num_2 total

06JAN2019  5  10   15
13JAN2019  5  10   25
20JAN2019 5   10   35
27JAN2019  5  10   45

[PeterClemmensen · Accepted solution]

Do like this

data have;
input date:date9. num_1 Num_2;
format date date9.;
datalines;
06JAN2019 5 10 
13JAN2019 5 10 
20JAN2019 5 10 
27JAN2019 5 10 
;

data want;
   set have;
   if _N_=1 then total=sum(num_1, num_2);
   else total=total+num_2;
   retain total;
run;

[novinosrin]

data have;
input date :date9.    num_1 Num_2 ;
format date date9.;
cards;
06JAN2019  5  10   
13JAN2019  5  10   
20JAN2019 5   10  
27JAN2019  5  10  
;

data want;
set have;
if _n_=1 then total+sum(num_1 ,Num_2);
else total+ Num_2;
run;