You must make the box very wide. InDesign will automatically update page numbers when you are through and it requires that the box could fit the number 1,999, even if your page numbers will remain low.
The shortcut on a Mac operating systems (OS) is to press “Command,” “Shift,” “Option” and the letter “N” at the same time. You should use this if you will be using this command a lot. The short cut on Windows OS is to press “Control,” “Shift,” “Alt” and the letter “N” at the same time. Your first number will appear as an “A” with a number sign next to it because it is the master page. The other page numbers will appear as numbers.