Best way to do this?

Hello,

I get a string as input that is a series of numbers.

If that string is any series of nines (one or more) then I must make the string equal to ten nines.

For example:

If string == "99998" then leave alone
If string == "19" then leave alone
If string == "9999" then make string = "9999999999"

Ideas?

Thanks!!
Mark