What is the syntax of creating an if statement for multiple ID's in a .tpl file?

I got this little piece of code: {if $smarty.get.id_cms == 1 } I would like for it to include every cms page with the id 1 to 20. Rather than creating 19 more if statements.

I tried to use "," and ";" without any success.

Using "," or ";" breaks the page into whiteness. Indicating that my 'guessed' syntax is wrong.