find first four if they are numeric

Hi!

I would like to find the first four positions in a column with SSIS ,s Derived column feature if all first four is numeric values. The columns datatype is unicode String [DT_WSTR].

Below is an example of how the column could look and i only would like to find first four charaters where all four is numeric. Anyone that has an solution to this?

Br

Arne

346a etc

9583desk l d l

etc etc etc

4568abc

Arne Olsson