Repeated addition is a tedious task in which an integer A is first written on a piece of paper with a plain pencil, and then the integer X is repeatedly added to the number on paper until that number becomes B.
Only one number is written on the paper at any given time. Addition is performed so that only digits that need changing are erased and replaced by new ones.
In order to estimate how many erasers will be needed, return the total number of digits erased if repeated addition is performed as above. The three integers will be given as three Strings.