Number

[Tim Starling]

I need to validate a code that is entered into a form and need to be able to strip certain numbers out of the ones submitted.  There will always be 4 numbers submitted but what would be the easiest way to take a set of numbers like 4765 and strip away the 1st, 2nd, and 4th number to just end up with the value of 6?  Or to strip the last two out and end up with 65?   Thanks, Tim