How to test if a string is inside a list of predinfined list of string in oracle pl/sql

I define a list a string which contains different country codes ( for example , USA ,CHINA ,HK ,JPN) How can I check that if a input variable equal to one of the country of the country list in pl/sql . I use the following code to test it but fail, how can I revise it?

declare country_list CONSTANT VARCHAR2(200) := USA,CHINA,HK,JPN; input VARCHAR2(200); begin input := 'JPN'; IF input IN (country_list) DBMS_OUTPUT.PUT_LINE('It is Inside'); else

     DBMS_OUTPUT.PUT_LINE('It is not  Inside');

END IF; end;

From stackoverflow

• If you can guarantee that the input will not include the delimiter, you can do this:

  country_list := 'USA,CHINA,HK,JPN';
  
  input := 'JPN'; -- will be found
  IF INSTR(',' || country_list || ','
          ,',' || input || ',') > 0 THEN
     --found
  ELSE
     --not found
  END IF;
  
  input := 'HINA'; --will not be found
  IF INSTR(',' || country_list || ','
          ,',' || input || ',') > 0 THEN
     --found
  ELSE
     --not found
  END IF;