Extracting a number

I need to write a subroutine in VB.NET 2003 which extracts numbers from a string (they will always be nonnegative integers). It must only extract numbers at the end of the string.

Examples:
=======

abc123 -> 123
123abc456 -> 456
123abc456def789 -> 789
123 -> 123
123abc -> nothing
abc123d -> nothing
abc -> nothing

Is there anything built into VB.NET 2003 that can do that? If not, can anyone show me the best way of implementing this subroutine?

Thanks