Part of my macro reads the last number in a string (URL). This number is stored in a variable. Then the value of the variable is to be increased by 1 (set variable to variable + 1).
This works wonderfully if there are no preceding zeros:
Using the Set Variable to Text action action, I added the prefix 9 to my variable Page like this: %Variable%Prefix%%Variable%Page%. After incrementing the result, I applied a simple regular expression (\d{1})(\d*) and used the second capture group (number without the prefix) to move on.