SAS Fill In Blanks With Retain Statement

So I am trying to retain values on SAS but with a condition that includes my ID field. I have the following dataset:

I want to retain provided the ID is the same and zero if its a dot, see results below:

How about the UPDATE trick.

data test;
   infile cards expandtabs;
   input id amount;
   cards;
1   230
1   450
1   .
1   .
2   .
2   .
;;;;
   run;
proc print;
   run;
data test2;
   update test(obs=0) test;
   by id;
   if first.id and missing(amount) then amount=0;
   output;
   run;
proc print;
   run;